UK Drinking Water Inspectorate Information

This document provides guidance on safeguarding the quality of public water supplies. It will be used as a reference document by the Drinking Water Inspectorate appointed by the Secretary of State for the Environment and the Secretary of State for Wales under Section 60 of the Water Act 1989 (HMSO 1989a) ('the Act'). Inspectors will be checking whether the various requirements concerning drinking water quality laid on water undertakers by relevant parts of the Act and the Water Supply (Water Quality) Regulations 1989 (HMSO 1989b) and the Water Supply (Water Quality) (Amendment) Regulations 1989 (HMSO 1989c) ('the Regulations') made under it are being met satisfactorily. Thus the document will be of major interest to water undertakers and to others with an interest in drinking water quality. However, it does not purport to offer any authoritative interpretation of the Regulations. From time to time it will be updated.

An explanation of the new legal regime in the Act and the Regulations relating to the quality of public water supplies is contained in a publication entitled, 'Drinking Water Quality in Public Supplies: An Explanation of the Water Act 1989 and the Water Quality Regulations 1989' (DOE 1989) prepared by the Department of the Environment. Copies may be obtained free of charge from the Drinking Water Division of the Department, Romney House, 43 Marsham Street, London SW1P 3PY.

The full titles of all documents referred to in this publication are provided in Annex 2.

1 Identification of Water Supply Zones

1.1 Water undertakers are required by Regulation 29 to prepare and maintain a record of water supply zones. As defined in Regulation 2 these zones are the basic units for establishing sampling frequencies, compliance with the standards and information to be made publicly available.

1.2 A reasonably consistent approach is needed in the selection of water supply zones, with sufficient flexibility being maintained for complex or unusual circumstances. Undertakers should therefore first identify whether an area is supplied from a single source or from more than one source. A source could be the outlet of a water treatment works, a borehole, a pumping station, a blending point or a service reservoir.

1.3 A single source which supplies a discrete area should always be recorded as a single water supply zone unless it normally serves a population greater than 50,000. In such circumstances the area must be sub-divided into water supply zones each with a population less than 50,000 (see definition of water supply zone in Regulation 2).

1.4 Any discrete area whether supplied by one or more sources should be sub-divided into separate supply zones if there are or could be significant differences in water quality within the area. Each zone would normally be served by an individual service reservoir or water tower, pumping or booster station, or would be distinguished as a separate pressure zone or by other appropriate features of the distribution system. In areas where the variations in water quality are complex or not predictable a convenient geographical boundary or an area served by an appropriate feature of the distribution system should be chosen to identify a water supply zone. Each zone should serve less than 50,000 people.

1.5 Temporary introduction of sources such as in an emergency or for limited periods during summer months should not influence the identification of water supply zones.

1.6 Each year, undertakers should review their delineation of water supply zones, although for year on year assessment of water quality the number of changes should be kept to a minimum.

2 Sampling Procedures and Identification of Sampling Points and Supply Points

(Parts IV and V of Regulations)

2.1 Part IV of the Regulations prescribes that water shall be sampled a certain number of times a year from points within the distribution system of each water supply zone chosen in such a way that, as far as is reasonably practicable samples taken from those points are representative of the water quality in the zone as a whole.

2.2 The sampling points for lead, copper, zinc and at least 50% of the sampling points for microbiological parameters and residual disinfectant must be selected at random. For all other parameters the Regulations allow for a choice between random sampling and sampling at fixed points. Preferably, the points should be chosen at random because over time this is likely to provide the best picture of water quality. However if the water undertaker is satisfied that samples taken from certain fixed points are representative of the concentrations of one or more of these parameters in the water supply zone as a whole that parameter or parameters may be sampled at those fixed points.

Sampling from random points

2.3 Random sampling points should be predetermined using one of the following methods:

Sampling from fixed points

2.4 Fixed sampling points should be predetermined and chosen in such a way that samples taken from them are representative, as far as is reasonably practicable, of the water quality throughout the zone. They should be changed only for good reason and then only at the start of a calendar year.

Sampling for lead, copper and zinc

2.5 The sampling points must be chosen at random. The sample taken should consist of the first 1 litre of water which issues from the consumer's tap (random daytime sample). Each sample should be analysed for lead, copper and zinc.

Sampling for microbiological parameters
Consumers' taps

2.6 Taps connected directly to the main at consumers' premises provide the most satisfactory means of sampling water in a water supply zone. Preferably, samples should be taken from consumers' taps selected at random but where this is not practicable up to fifty per cent of samples in a water supply zone may be taken from fixed points. Where possible, samples should be taken from metal taps which are disinfected before sampling and which are sampled in such a way as to give representative samples of the water quality supplied to consumers' taps. Where only plastic taps or mixer taps are available they should be cleaned and disinfected before sampling. All external fittings such as anti-splash devices and hoses should be removed before sampling. Internal inserts should be removed where possible.

Treated water leaving treatment works

2.7 Under Regulation 17, sampling is required from the point at which water leaves each treatment works. These points should be located so as to provide a representative sample of the water flowing into distribution. All treatment Works outlets should be fitted with metal sampling taps of a hygienic design which do not have attachments or inserts and which are made from materials complying with BS 6920 (BSI 1988). Water should be supplied to the sampling tap through a sample line of a suitable material (if plastic, complying with BS 6920) which should be as short as possible.

Before a sample is taken, sample taps shuld be allowed to run for at least 2 minutes or as long as it takes to clear water standing in the sample line. Measurement of temperature can be used to determine when the standing water has been cleared.

Service reservoirs and water towers

2.8 Under Regulation 18, sampling is required from service reservoirs and water towers. Where reservoirs are divided into compartments, each compartment should be treated as a separate reservoir and sampled accordingly unless the compartments are inter-connected. Similarly, where there are 2 or more service reservoirs on a site, they should be sampled separately unless they are inter-connected. Preferably, all service reservoirs and water towers should have proper metal sampling taps, as described in 2.7, fitted at the outlet for sampling. Where it is impossible to provide a tap on site, a tap should be provided on the outlet main at the nearest possible point to the reservoir or tower. As an interim measure, pending provision of a proper sampling point, a consumer's tap (see paragraph 2.6) at a property fed directly from the outlet main should be used. Dip sampling should not be used for compliance sampling.

Hydrants, meter boxes and standpipes

2.9 When it is not possible to obtain a sample from a consumer's tap connected directly to the main and it is necessary to obtain a sample for operational or investigational purposes the sample may be taken directly from the main by means of a standpipe constructed for that purpose and attached to a hydrant or meter box on a flow-through main. The standpipe should be cleaned, stored and transported in a clean plastic bag, disinfected immediately prior to connection, flushed and then disinfected again. Flushing should be at a rate which avoids disturbance of deposits in the main. After use the standpipe should be cleaned and stored in a clean plastic bag.

Authorisation of supply points

2.10 Regulation 12 provides that the Secretary of State, upon written application of a water undertaker, may authorise sampling for certain specified parameters from a supply point (ie from a treatment works or a service reservoir) instead of from sampling points (ie consumers' taps) if he is satisfied that this is unlikely to produce significantly different data in respect of the parameters in question. Inspectors will need the following formation when considering applications:

Such authorisation will not be possible for a zone in which blending of waters of different quality takes place unless the water undertaker can demonstrate with sufficient data that the different waters contain similar and relatively constant concentrations of the respective parameters.

Sampling Procedures

2.11 Regulation 21 sets out the general principles of sampling procedures to be applied.

All parameters (except microbiological)

2.12 Water undertakers should have set out in a sampling manual the procedures and precautions to be adopted for each parameter or group of parameters. As a minimum this should cover:

2.13 Further general information on sampling procedures is given in the publications 'General Principles of Sampling and Accuracy of Analytical Results' (HMSO 1980a) and 'General Principles of Sampling' (HMSO 1989d). Detailed information for individual parameters or groups of parameters is given in the individual booklets in the series 'Methods for the Examination of Water and Associated Materials' published by the Standing Committee of Analysts (HMSO 1976 onwards).

Microbiological parameters

2.14 Water undertakers should have set out in a sampling manual the procedures and precautions to be adopted during sampling. As a minimum this should make clear that:

2.15 Samples should be kept cool using ice packs or equivalent when necessary and transported in the dark in sealed insulated boxes, which should be regularly cleaned and disinfected. Microbiological examination of the water sample should be undertaken as soon as possible after collection. Every attempt should be made to start the examination within six hours of sample collection. Where logistics do not allow this, samples may be examined up to 24 hours after collection provided they are kept cool (2-10°C) and in the dark.

2.16 Further details of recommended sampling procedures are given in Report 71 (HMSO 1982), now being updated.

Situations when increased sampling frequencies apply

3.1 Regulations 13 and 19 prescribe among other things that increased sampling frequencies shall apply when, as a consequence of a change in the treatment of water, an undertaker considers that a standard for a parameter has been or may be contravened. The following circumstances amongst others may give rise to this:

Examples		Parameters
(1) any supply zone fed from a source where the treatment has been changed significantly.		parameters whose concentration alters during treatment, or which are present in coagulants eg aluminium or iron.
(2) any supply zone fed from a newly commissioned treatment works or an existing treatment works when a new process has been commissioned.		parameters whose concentration alters during treatment.
(3) any supply zone fed by a blend of sources where blending is designed to ensure compliance with a prescribed standard.		relevant parameters eg nitrate, fluoride.
(4) any supply zone in which mains re-lining has been carried out recently.		relevant parameters eg pH value and aluminium from cement mortar re-lining in areas with water of low alkalinity.

Authorisation of reduced sampling frequencies

3.2 Regulation 13(6) provides that the Secretary of State may, upon written application of a water undertaker, authorise a reduced number of samples to be taken from consumers' taps in the calendar year 1990. The written application should include the following information:

In Assessing an application an Inspector should take into account all relevant material including the amount of data available and the difference between the actual concentrations or values and the prescribed concentration or value.

3.3 Regulation 13(5) allows for reduced frequencies in 1991 and 1992 provided that the Secretary of State is of the opinion that concentrations of parameters will not increase to a significant extent and has so notified undertakers. Similar information to that in the previous paragraph will be required to enable Inspectors to assess applications.

3.4 Regulation 17(4) provides that the Secretary of State may, upon written application of a water undertaker, authorise a reduced number of samples to be taken from water leaving treatment works in the calendar year 1990 for analysis for total and faecal coliforms and colony counts. Applications should include the following information to enable assessments to be made:

In assessing an application the Inspector should take into account all relevant material including the amount of data available, the risk of coliforms being present in the treated water and the variability of colony counts.

Operational sampling

3.5 For some parameters more frequent sampling and analysis, and in some cases continuous monitoring, will be needed for operational purposes at the treatment works.

Individual parameters

3.6 Where fluoride is added to a water supply at the request of the health authority, the agreement between the water undertaker and the health authority will determine the sampling frequency. In most cases the agreement will accord with the Code of Practice on Technical Aspects of Fluoridation of Water Supplies (HMSO 1987).

3.7 Each water undertaker is required to develop a monitoring strategy for pesticides based on the likely risk of particular pesticides being present in the water source serving the zone. In developing a monitoring strategy water undertakers are advised to:

Information on pesticide use and properties is given in WP/18/1989 appended to this document.

3.8 On the basis of that strategy each water supply zone should be monitored at the frequency prescribed in Part IV of the Regulations for each pesticide identified as likely to reach that zone. Atrazine and simazine, which are widely used in non-agricultural situations, should be monitored in all water supply zones. Footnote (i) to Table 3 of Schedule 3 of the Regulations links the requirement to increase sampling and the permission to reduce sampling only to the particular pesticide concerned.

Timing of sampling

3.9 For each parameter the specified number of samples should be taken in the water supply zone, at the treatment works and from service reservoirs at regular intervals throughout the year to detect any seasonal variations in water quality. In some circumstances water undertakers may need to take additional samples for some parameters for operational purposes to determine the extent of seasonal variations in water quality.

4 Performance Required of Analytical Systems

Non-microbiological parameters

4.1 Regulation 21(2)(d)(iii) specifies that the analytical systems and methods used should be capable of establishing within acceptable limits of deviation and detection whether the sample contains concentrations or values which contravene the standards.

General specification of acceptable limits of deviation and detection of individual analytical results

4.2 For most parameters, the maximum tolerable errors of individual analytical results are specified as follows:

and where the terms 'total error', 'total standard deviation', 'systematic error (or bias)' and 'limit of detection' have the meaning ascribed to them in The Chemical Analysis of Water, General Principles and Techniques', (Hunt and Wilson 1986).

4.3 This form of specification implies a limit of detection (4.645 times the within-batch standard deviation of results for blanks) equal to C, or one-tenth of the prescribed concentration or value.

4.4 Because of the nature of some parameters the above form of specification is not appropriate. Specifications for these parameters are given below.

Total error not more than + 0.2 pH units.
Total standard deviation not more than + 0.05 pH units.
Systematic error not more than + 0.1 pH units.
For water of conductivity less than 100µS/cm these criteria are increased by
a factor of 2.

Current methods are not capable of achieving a target total error of less than + 20% for individual hydrocarbons or phenols. Laboratories are expected to use the best currently available methods, eg the methods published by the Standing Committee of Analysts. Further comments on the analysis for these parameters are made in paragraph 5.4.

This parameter consists of the sum of the concentrations of four individual substances: trichloromethane, dichlorobromomethane, chlorodibromoomethane and tribromomethane. For this parameter, for individual substances, C is one-fortieth of the prescribed concentration.

Current methods are not capable of achieving a target total error of less than + 20% for many individual substances. Laboratories are expected to use the best currently available methods, eg the methods published by the Standing Committee of Analysts. Total pesticides should be regarded as the sum of the detected concentrations of individual substances. It is not possible to specify a total error requirement for total pesticides.

The prescribed concentration is the sum of the detected concentrations of six specified individual polycyclic aromatic hydrocarbons. It is not possible to specify a total error requirement for this parameter. For individual substances (except benzo 3.4 pyrene) C is one-fiftieth of the prescribed concentration. For benzo 3.4 pyrene C is 1ng/l.

Microbiological Parameters

4.5 Good laboratory practice and analytical quality control are essential to achieve satisfactory results.

4.6 It is not possible to specify a performance for methods for microbiological parameters in terms of total error or limit of detection. However, the methods described in Report 71 (HMSO 1982) will be capable of the required performance. If alternative methods are used, they must be shown to be capable of producing equivalent or better performance by means of interlaboratory trials.

4.7 Any method used for the detection of indicator organisms must be capable of detecting the presence of small numbers of such organisms (even if they have been damaged in their environment or by the disinfectant), even as few as one in the appropriate sample volume, because false-negative results can have important consequences. Conversely, the methods used must be subject to good microbiological practice to ensure that contaminating organisms are not inadvertently introduced into the detection process. To avoid mis-identification of organisms, the methods used should be checked against standard reference procedures or against known strains of bacteria. Such strains should be selected and maintained in a manner that ensures their suitability for the purpose.

5 Analytical Methods

All parameters (except microbiological)

5.1 In general, the methods published by the Standing Committee of Analysts in the series 'Methods for the Examination of Waters and Associated Materials' (HMSO 1976 onwards) will be capable of the performance required for determining compliance with the prescribed concentrations or values in the Regulations. However, laboratories must take steps to ensure adequate analytical quality control (see Chapter 6).

5.2 The prescribed concentration or value relates to the total amount of a parameter present in a sample (in solution and as suspended or collodial material) unless otherwise specified in paragraph 5.4 below.

5.3 There are some parameters in the Regulations that are difficult to determine or interpret because:

It follows from (c) that the analytical method must be used consistently by all laboratories.

Some other parameters may adequately include or represent another parameter or parameters, in which case determination of the representative parameter only is required.

5.4 The parameters which fall into these categories are set out in the following paragraphs together with recommendations and comments.

Determination of colour should be performed on samples which have been passed through a 0.45 µm filter. Visual comparison of colour intensity of samples against inorganic colour standards or calibrated permanent g1ass standards provides a direct determination of compliance with the prescribed value. An indirect method of measurement of the absorbance of the sample in 40 mm cells at a wavelength of 400nm using a spectrophotometer may be used; the absorbance reading has to be related to inorganic colour standards (Pt/Co) and this may be achieved by calibrating the spectrophotometer using such colour standards. The procedures described in the SCA methods (HMSO 1981a and HMSO 1988a) should be followed.

This parameter includes suspended solids which do not require separate measurement. Determination of turbidity should be performed by a method which measures turbidity as formazin turbidity units. These units are equivalent to Jackson turbidity units and to nephelometric turbidity units. The procedures described in the SCA method (HMSO 1981a) should be followed.

The odour parameter includes hydrogen sulphide which does not require separate measurement. Odour and taste of water are closely linked. When water has an odour it almost invariably has taste; however an odourless water may have distinct taste. Determinations of odour and taste of water rely upon subjective assessments. Water undertakers are required to carry out frequent qualitative and less frequent quantitative determinations of odour and taste (Tables 1 and 2 respectively of Schedule 3 to the regulations). The methods published by SCA (HMSO 1980b) should be used.

In the qualitative method the analyst smells or tastes a water sample at ambient temperature and classifies any odour or taste in terms of intensity and nature. This method will detect any chlorinous odours and tastes. Long-standing experience shows that consumers also assess qualitatively the odour and taste of their water supply for complaints about drinking water quality frequently concern odour or taste, particularly chlorinous odours and tastes. Water undertakers are expected to record all odour and taste complaints received from consumers. They are also expected to investigate persistent complaints and where practicable take appropriate remedial action.

The quantitative method involves the determination of the threshold odour or taste number. Only samples which have been dechlorinated should be used to determine compliance with the quantitative standards in the Regulations. The intensity of odour or taste is determined as a threshold number by each person on a panel of assessors. The threshold odour or taste number of the sample is the geometric mean of the individual results. This procedure reduces the subjectivity of the assessment. Because samples are dechlorinated before being tested the method measures any 'natural' or underlying odour or taste of the water and will not include most chlorinous odours or tastes. The quantitative odour determination has to be carried out in samples at 25°C to determine compliance with the standard in the Regulations and not at 40°C as recommended in the SCA method. A threshold odour or taste number obtained by the SCA method is converted to a dilution number (the unit of measurement given in the Regulations) by subtracting one. Thus a threshold number of 4 is equivalent to a dilution number of 3.

This parameter is usually refered to as permanganate value (PV) or permanganate index (PI). The determination of PV or PI is empirical and many different procedures can be used. Therefore, the precise conditions of test have to be specified in order to define the parameter and to ensure comparability of results between laboratories. PV or PI is a measure of the amount of oxygen taken up from permanganate by an acidified and heated sample under the specified conditions of test. A procedure published by SCA (HMSO 1983), involving boiling for 10 minutes with 0.002M potassium permanganate, should be followed exactly. Other methods published by SCA (HMSO 1983) may also be valid, provided users have established a conversion factor.

The analytical method has a limit of detection greater than the prescribed concentration of 1 mgN/l. Routine examination of samples for Kjeldahl nitrogen is not required. If the analysis of a water sample shows unusually high colour, permanganate value or total organic carbon, analysts may carry out Kjeldahl nitrogen determination to assist in identifying the likely source of the increased amount of organic substances in the sample.

This parameter, which derives from the EC Drinking Water Directive, includes all substances extracted by chloroform under the conditions used in the analytical method. The method is non-specific as it does not identify the specific substances extracted. This parameter does not provide useful information about water quality hence routine examination of samples is not required.

This parameter includes all hydrocarbons extracted by petroleum ether. The analytical method has a limit of detection greater than the prescribed concentration of 10 µg/l. Routine examination of samples for dissolved or emulsified hydrocarbons is not required. However the presence of hydrocarbons in water is undesirable for aesthetic reasons. If hydrocarbons are present in significant quantities this may be apparent from the appearance of the water or from qualitative or quantitative tests for odour and taste. If hydrocarbons are thought to be present, the analyst may determine individual hydrocarbons (eg benzene and toluene, but not polycylic aromatic hydrocarbons) to assist in determining the origin of the hydrocarbons and any appropriate action that may be needed.

This parameter includes all phenols. Phenols and their chlorinated derivatives can give rise to taste and odour. If the qualitative or quantitative tests for odour and taste suggest that phenols may be present the analyst may determine individual phenols (eg phenol, methyl phenols and chlorinated derivatives) to assist in determining the origin of the phenols and any appropriate action that may be needed.

This parameter is specifically concerned with substances reacting with methylene blue. The analytical method used should be based on complexation of the anionic surfactants with methylene blue in alkaline solution followed by extraction of the complex into chloroform and spectrophotometric determination. The method should be calibrated by standard solutions of lauryl sulphate or other specific anionic surfactants for which a conversion factor to lauryl sulphate has been established. The method published by the SCA (HMSO 1981b) is not based on lauryl sulphate and therefore a conversion factor is required.

This parameter is covered by the conductivity parameter and provided conductivity determinations are carried out on water samples, specific determination of dry residues is not necessary.

This refers to free cyanide and easily liberable cyanide. The method published by the SCA (HMSO 1988b) should be used.

This parameter is defined as the total concentration of free ammonia and ammonium ions. Most waters contain ammonia and ammonium ions equilibrium with each other. The parameter is often referred to as ammoniacal nitrogen or total ammonium. One of the methods published by the SCA (HMSO 1980c) should be used.

This refers to orthophosphates and acid hydrolysable polyphosphates and metaphosphates. The method published by the SCA (HMSO 1980d) should be used.

Microbiological parameters

5.5 The microbiological parameters included in the Regulations should be understood as having the following descriptions:

Coliforms are members of a genus or species within the family Enterobacteriaceae, capable of growth at 37°C, and normally possessing ß-galactosidase.

Faecal coliforms are thermotolerant coliform organisms which are capable of growth and of expressing their fermentative properties at 44°C.

Faecal streptococci are Gram-positive cocci, forming pairs and/or chains which are non-sporing, oxidase and catalase negative, possess Lancefield's Group D antigen and can hydrolyse aesculin. They can grow under aerobic and anaerobic conditions in the presence of bile salts and in concentrations of sodium azide which are inhibitory to coliform organisms and most other Gram-negative bacteria.

Sulphite-reducing clostridia are Gram-positive, anaerobic, spore-forming rods which reduce sulphite to sulphide. This group is typified by Clostridium perfringens which produces a stormy fermentation in milk. The standard for sulphite-reducing clostridia is 1 organism or less in a 20ml sample examined using a multiple tube method. Report 71 includes a multiple tube method and a membrane filtration method both of which estimate the number of organisms in a 100ml sample. A result of 5 organisms or less in 100ml of sample obtained by either method is regarded as equivalent to 1 organism or less in a 20ml sample.

5.6 The methods for examination of the organisms described in paragraph 5.5 should be those described in Report 71 (HMSO 1982) and any subsequent revisions. Where daily sampling of water leaving treatment works is required, test kits, which determine simply whether an indicator organism is present or absent in 100ml of sample, may be used for one or two sampling occasions per week but no more. If the test kit indicates the presence of an indicator organism the procedures set out in paragraph 7. 7 should be followed and any further samples examined using the standard methods described in Report 71.

5.7 For technical and epidemiological reasons, the direct search for pathogenic bacteria or other pathogenic micro-organisms such as viruses and cryptosporidia has no place in the routine microbiological examination of water supplies. There are occasions, however, when an investigation for faecal pathogens may be necessary - for example, when a water supply is suspected of transmitting disease. In such cases there must be close liaison with relevant officers of the appropriate local authorities, the medical officer with responsibility for environmental health and the Public Health Laboratory Service to ensure that efforts are directed to the most likely causal organisms. Amongst the organisms which may need to be sought by a competent laboratory service are salmonellas, shigellas, cryptosporidia, campylobacters, giardia, aeromonads, enteric viruses, vibrios, and pathogenic amoebae. Water policy letters WP/6/1989 and WP/15/1989 (see Annex l) give advice on cryptosporidia.

(Regulation 21)

6.1 Regulation 21(2)(e) specifies that any laboratory analysing samples to determine compliance with the standards prescribed in the Regulations should have a system of analytical quality control that is periodically subjected to checking by a person approved by the Secretary of State. Departments are still considering the procedure whereby a person can be approved for this role and will advise water undertakers in due course.

Non-microbiological parameters

6.2 For internal quality control, laboratories are expected to carry out the following procedures in sequence and obtain satisfactory results before using any analytical system to determine compliance with the standards prescribed in the Regulations:

The results of both the preliminary tests and the control charts should be available for inspection.

6.3 Laboratories will also be expected to participate in external quality control schemes where available, involving the distribution of check samples The results should be available for inspection. Any evidence obtained by such participation showing that analytical errors exceed those specified in Chapter 4 for the parameter in question should trigger immediate investigation and remedial action. The form of such investigation and action will depend on individual circumstances. However, for para- meters which give rise to continuing problems in meeting the accuracy requirements and whose levels approach the prescribed concentration, laboratories may need to conduct detailed development work on their analytical system, and more detailed analytical quality control.

Microbiological parameters

6.4 It is necessary for successful microbiological examinations to be able to demonstrate the presence or absence of a particular class of micro-organism in a given sample volume and to estimate numbers. The detection of small numbers is particularly Currently recommended methods require culture of the organism to achieve detection so the culture medium used must be shown to be capable of supporting the growth of the appropriate organism. Because of the ubiquitous nature of most microbes, it is essential to ensure that any that are detected have originated from the original sample and have not been introduced inadvertently during sampling or in the laboratory.

6.6 Laboratories will also be expected to participate in external quality control schemes, where available, involving distribution of check samples. Any evidence obtained by such participation showing deficiencies in the procedures should trigger immediate investigation and remedial action.

6.7 As accurate laboratory results are dependent upon the quality of the received sample, the appropriate technique for obtaining a suitable sample must be strictly adhered to (see paragraphs 2.6-2.9 and 2.14-2.16).

7 Action if Quality Standard Infringed

7.1 Water undertakers have given a number of undertakings under Section 20(5)(b) of the Act to take particular steps to secure or facilitate compliance with the quality standards where they are being infringed. The Departments have also granted a number of relaxations of some of the standards under Regulation 4, some of which are time limited. Undertakings and relaxations afford undertakers relief from enforcement action under Section 20. However there will be other situations, not covered by an undertaking or a relaxation, where a sample is taken indicating an infringement of a standard. This chapter provides guidance on the action to be taken by the undertaker in such situations.

7.2 For most parameters standards apply to each sample taken. If a standard is infringed, that water is unwholesome unless a relaxation has been given. This does not necessarily mean that water in the whole supply zone is unwholesome or even that water at the point where the sample was taken remains unwholesome. Only further sampling will determine that. This is relevant to the Secretary of State's obligation to take enforcement action where he is satisfied that a standard is continuing to be infringed or that it was infringed and it is likely to be so again (Section 20(1)). It is also relevant to his consideration of whether an infringement of a standard is 'trivial' and therefore whether he may disregard it under Section 20(5)(a).

7.3 lf an undertaker is not clear whether an infringement falls within the terms of the previous paragraph, it should consult the appropriate Department. The procedure set out in Table 7.1 should be followed as a general guide in the event of an infringement of any standard. In addition the following action should be taken in relation to the circumstances specified.

Any significant water quality failure

7.4 A 'significant' failure cannot be defined, but examples of microbiological and chemical failures are given in paragraphs 7.8, 7.9 and 7.12. When significant failures occur there should be a presumption that water in supply is a potential health hazard, in which case water undertakers should immediately obtain expert advice. Speed will be of the essence so it follows that water undertakers must have standing arrangements for obtaining expert advice on toxicological and microbiological matters either from individual experts or from centres of expertise. When such an incident occurs water undertakers will be expected to -

7.5 If any such incident could involve significant health risks to consumers the Department of the Environment or Welsh Office should be notified as soon as possible in accordance with agreed procedures.

Any standard infringed owing to fittings in ownership of consumer

7.6 Where a standard is infringed solely because of the state of fittings in the ownership of a consumer, the water undertaker will inform the consumer so that he may take remedial action. When there is a significant health risk the local authority would also be informed in accordance with agreed procedures.

Microbiological standard infringed

7.7 Further investigation has to be instigated the same day when 'presumptive' coliforms are detected in any sample taken from treatment works, service reservoirs, water towers or consumers' taps. As a minimum this should indude:

No further action is necessary if the investigation at (b) does not confirm the presence of coliforms or faecal coliforms but the results of the additional operational samples and checks should be recorded.

7.8 If these investigations show evidence of actual or potential microbiological contamination, then effective remedial action should be instituted immediately to ensure that satisfactory microbiological conditions are restored. This is particularly important if large numbers of coliforms or any faecal coliforms are detected. The action will depend on local circumstances but it could include, where appropriate:

In some cases the remedial action may be of a short-term nature pending the completion of longer term measures.

7.9 If any evidence is detected of actual or potential serious microbiological contamination, such as high counts of faecal coliforms, the presence of specific pathogens or failure of the disinfection or filtration processes, then urgent action must be taken including that specified in paragraph 7.4.

7.10 If intermittent and related low-level failures for total coliforms are detected anywhere in the system (for example failure when there is heavy rain or failures in the same place at the same time each year) water undertakers should establish the cause and take remedial action. Remedial action must be taken in respect of each zone where more than 5% of samples contain coliforms (Regulation 3(6)) and where a similar degree of non- compliance is found at a service reservoir or water tower. Such programmes of remedial action should be submitted as soon as possible to the Department of the Environment or the Welsh Office as appropriate in the form of an undertaking under Section 20(5)(b) of the Act.

7.11 Continuous review is needed of colony counts in routine samples taken from treatment works, service reservoirs and water supply zones. Further investigation and, where appropriate, remedial action should be taken when:

Chemical standard temporarily infringed owing to emergency or operational difficulties

7.12 Short-term infringement of standards may occasionally occur because of operational difficulties at a treatment works or in the distribution system or following a pollution incident. Examples are:

Chemical standard infringed regularly or chronically

7.13 If a standard is infringed in any of the following circumstances, unrelated to emergencies, operational difficulties or a specific pollution incident:

to avoid enforcement action under Section 20 of the Act, a water undertaker should either seek a relaxation under Regulation 4 or should offer an undertaking under Section 20(5)(b) to take appropriate steps to secure or facilitate compliance.

Pesticide standard infringed

7.14 The maximum admissible concentration for this parameter in the EC Directive was set to minimise the occurrence of pesticides in drinking water and is not based on toxicological evidence. The Government is pressing the European Commission for a review of the pesticide parameter. Advisory values have been calculated in the UK for some pesticides from published toxicological data and with a wide margin of safety. The current values are set out in WP/18/1989 (Annex 1), where their derivation and significance are explained. They will be reviewed as new evidence becomes available. The values are reproduced in Table 7.2.

7.15 If a pesticide concentration in the water leaving a treatment works or in distribution exceeds the prescribed concentration of 0.1ug/l, the water undertaker should re-sample the water immediately. If after re-sampling infringement of the standard is confirmed, it should take the following action:

7.16 If the re-sampling and subsequent routine sampling establish that infringement of the standard was transient or trivial, or if the cause of the infringement is discovered and is unlikely to recur, no further action is needed. However, where there is continuing infringement of the standard,the undertaker should submit an undertaking to the appropriate Department under Section 20(5)(b). If the infringement does not approach or exceed the relevant advisory value in Table 7.2 the terms of the undertaking should be to investigate potential treatment methods to determine whether a significant reduction in concentration can be achieved and, in the light of these investigations, install treatment or take other remedial action where appropriate.

7.17 If a pesticide concentration in supply not only infringes the standard but also approaches or exceeds the advisory value in Table 7.2 for that pesticide that should be regarded as a significant infringement in terms of paragraph 7.4 and the water undertaker should take immediate action in accordance with that paragraph. This will include re-sampling and may include the temporary provision of an alternative supply of potable water. In all cases the appropriate Department should be consulted on measures to be taken. lf sampling and investigation show that the pollution is of a more long-standing nature, and the concentration cannot be reduced below the advisory value immediately the undertaker should also submit an undertaking to the appropriate Department under Section 20(5)(b) to facilitate or secure compliance with the standard and in any case to reduce the concentration permanently below the advisory value as soon as practicable.

7.18 The advisory value for aldrin/dieldrin is lower than the standard in the Regulations. If such a value is exceeded in a supply but the standard is not infringed the undertaker should treat the matter on the same basis as paragraph 7.4 and also consult the appropriate Department on measures to be taken.

This information will most appropriately be provided at the same time as the annual report required by Regulation 31 is published.

Standard infringed for other reasons

7.20 Occasional infringements of standards may occur which are not covered by the preceding paragraphs. In these cases the procedure set out in the relevant parts of the Table 7.1 should be followed.

7.21 Increased programmed sampling should be instigated in accordance with the criteria set out in the Regulations.

Emergency procedures

7.22 It is important that water undertakers have written contingency arrangements to deal with emergencies. All staff should be familiar with them and procedures should be rehearsed from time to time. Each undertaker should review its arrangements regularly to ensure that they are up-dated to take account of its own emergencies and those that affect other undertakers so far as details become generally known. Hazard study techniques should be considered, if this has not been done already.

7.23 Undertakers should refer to the following documents on emergencies and implement their recommendations where relevant:

Table 7.2 Advisory Values for some Pesticides^*

Pesticide	Advisory Value µg/l

Aldrin and dieldrin	0.03
Atrazine	2
Bromoxynil	10
Carbendazim	3
Carbetamide	500
Carbophenothion	0. 1
Chlordane (total isomers)	0.1
Chloridazon	50
Chlormequat	10
Chlortoluron	80
Clopyralid	100
2,4-D	1000
DDT (total isomers)	7
Dicamba	4
Dichlorprop	40
Difenzoquat	80
Dimethoate	3
EPTC	50
Gamma HCH	3
Glyphosate	1000
Heptachlor/heptachlor epoxide	0.1
Hexachlorobenzene	0.2
Ioxynil	10
Isoproturon	4
Linuron	10
Malathion	7
Mancozeb (maneb plus zinc oxide)	10
Maneb	10
MCPA	0.5
MCPB	0.5
Mecoprop	10
Metamitron	40
Methoxychlor	30
Paraquat	10
Prometryn	10
Propazine	20
Simazine	10
Triadimefon	>10
Triallate	1

^* The derivation and significance of these values are given in WP/18/1989 (Annex 1)

8 Action where Risk of Water becoming Unwholesome after leaving Undertakers' Pipes

(Regulation 24)

8.1 Under Regulation 24, a water undertaker has certain duties relating to the supply of wholesome water when there is a risk that the water may not comply with the standards for lead, copper or zinc after it has left the undertaker's pipes and passed through lead, copper or galvanised iron pipes on consumers' premises. Whenever practicable, a pH value greater than 6.5 should be maintained in the water delivered to consumers, so that the water is not unduly aggressive towards these plumbing materials.

Lead

8.2 Regulation 24(1) refers to the risk that the water may cease to comply with the standard for lead of 50ug/l after leaving the water undertaker's pipes. Water undertakers should assume that there is a risk of a failure to meet the standard for lead in samples taken from consumers' taps in all their water supply zones, unless evidence is available that there is no such risk. In many zones this evidence of no risk will already be available from previous monitoring programmes in which random daytime samples (the first water which issues from the tap at any time during the day) have been taken from randomly selected properties supplied through lead pipework. The evidence should be derived from a minimum of 20 samples, but preferably 50 samples or more, taken regularly throughout a period of at least 1 year with a relevant proportion of samples having been taken during the summer months when water temperatures are at their highest and lead concentrations are likely to be at a maximum. If all such samples taken in a water supply zone are shown to comply with the 50 ug/l standard the water undertaker may assume that there is no risk of exceeding the lead standard in that zone. If previous monitoring programmes are not adequate to provide sufficient evidence, it may be obtained by carrying out before 30 June 1991 a survey over a period of at least 1 year in which a minimum of 20 samples, but preferably 50 samples or more, are taken in a water supply zone.

8.3 Where a risk has been identified, all water of low alkalinity (less than about 50 mg CaCO3/l) should have pH adjustment and control to maintain a pH value at or near to 8.5 and preferably not below 8.0 at consumers' taps, as this will bring about a significant reduction in lead concentrations (Lead in Potable Water, Technical Note No 5, DOE 1984). Water undertakers should determine whether a further significant reduction in lead concentration could be achieved by additional treatment of the water, for example by dosing with an orthophosphate. For waters of alkalinity greater than about 50 mg CaCO3/l, water undertakers should determine whether a significant reduction in lead concentration could be achieved by water treatment, for example by pH adjustment and control or by the addition of an orthophosphate.

8.4 The effectiveness of treatment in achieving a significant reduction may be determined for example by testing the water in an on-site rig using 2 metre lengths of conditioned, new lead pipe. (Guidance on the construction and operation of a rig is in preparation and Departments will advise water undertakers of its availability in due course.) In this test, the concentration of lead is determined in water samples taken from the rig before and after the proposed treatment. The test rig is designed so that the samples taken represent water which has been in contact with the pipe for 30 minutes. Alternatively, the effectiveness of treatment may be determined in a field trial carried out in a small part of a zone whereby lead concentrations in 30 minute stagnation samples taken from consumers' taps are measured before and after the introduction of treatment.

8.5 Where a risk has been identified, water undertakers should submit undertakings under Section 20(5)(b) to investigate whether a significant reduction in concentrations could be achieved by a reasonably practicable treatment and, if so, to install treatment as soon as practicable.

8.6 Regulation 24(4)(a) does not require an undertaker to treat water in any zone where treatment is unlikely to achieve a significant reduction in lead concentration. To provide some consistency in deciding whether a significant reduction would be achieved, the following guideline should be used. As a general rule, a reduction of 30% or more with a minimum reduction of 10 µg/l in the average lead concentration in 30 minute stagnation samples taken from the test rig or consumers' taps may be regarded as a significant reduction in the concentration of lead following the treatment. For example, if the lead concentration before treatment is 60 µg/l, a reduction to 42 µg/l or lower concentration after treatment would be regarded as significant, and if the lead concentration before treatment is 20 µg/l a reduction to 10 µg/l and not to 14 µg/l would have to be achieved to be regarded as significant.

8.7 Regulation 24(4)(b) does not require an undertaker to treat water in any zone where the prescribed risk relates only to water supplied in an insignificant part of the zone. Where less than 5% of the total population or, in any case, not more than 1000 people (approximately 400 properties) in the zone are supplied through lead pipes, the risk may be regarded as relating to an insignificant part of the zone.

8.8 The risk may also be regarded as relating to an insignificant part of the zone when either:

8.9 For any zone with less than 250 population (approximately 100 properties) the water undertaker should consider whether it would be more practical to promote a policy of lead pipe replacement whereby the water undertaker replaces its part of the lead service pipe and the householder replaces the remainder of the service pipe than to treat the water passing into that zone.

8.10 Regulation 24(4)(c) does not require an undertaker to treat water if treatment is not reasonably practicable. In many circumstances treatment involving the simple addition of a chemical to the water supply, such as pH adjustment using lime, sodium hydroxide or other alkalis or phosphate dosing using orthophosphoric acid or one of the sodium orthophosphates, will be regarded as reasonably practicable. pH adjustment by passing water through a filter containing calcined dolomite or similar material may also be considered reasonably practicable. Other treatment such as alternating the supply of waters of different plumbo-solvency may also be practicable in some circumstances.

8.11 The causes of particulate lead in water supplies have not been fully elucidated. In some cases particulate lead may be caused by the quality of water put into supply, currently or in past years. Problems due to particulate lead should be reduced as water undertakers improve the aesthetic quality of water leaving treatment works and rehabilitate the mains in the distribution systems. A specific treatment to reduce particulate lead is not available at present.

8.12 In addition to the requirement in Regulation 24(1)(b), there are some situations where the water undertaker should consider replacing its part of lead service pipes. These could include the following -

8.13 The occupier and the local authority environmental health officer (EHO) should be informed if a random daytime sample (see paragraph 2.5) from a property has exceeded the standard for lead. Advice should be given to draw off water which has been stationary in pipework before drawing water for drinking or cooking (Lead in Potable Water, Technical Note No2, DOE 1980). If the water undertaker is installing or planning to install treatment to reduce plumbo-solvency, then the occupier should be advised that a reduction in the concentration of lead would be expected when this treatment has been introduced. If the water undertaker is already carrying out all reasonably practicable treatment to reduce plumbo-solvency or treatment is not planned because the risk relates to an insignificant part of the zone, the occupier should be informed of this situation. Occupiers should be advised that if the lead pipes on their property leading to the drinking water tap are replaced, the water undertaker will replace its section of the lead service pipe if requested to do so (in accordance with Regulation 24(1)(b)).

8.14 If no lead plumbing is present in the property and the infringement of the lead standard is thought to be due to galvanic corrosion of lead solder in copper plumbing, no remedial treatment is at present possible. In the circumstances the occupier and EHO should be informed of the situation which may be expected to improve with time. The property should be sampled again a year later. If concentrations are still above 50 µg/l the holder and EHO should be informed that replacement of the lead soldered joints is advisable.

8.15 Water undertakers may assume that there is no risk of the standards for copper and zinc being exceeded unless there is evidence to the contrary. If routine random daytime samples from consumers' taps indicate failure to meet the standard for copper and zinc in a water supp1y zone the cause of any failure should be investigated. If any failure is not related to the particular circumstances of the property, and failures occur elsewhere in the zone, water undertakers should consider what action could be taken to ensure compliance. An appropriate undertaking under Section 20(5)(b) should then be submitted. The occupier (and the EHO) should be informed if a random daytime sample from a property has exceeded the standard for copper or zinc.

9.1 Section 52(1)(b) of the Act places a duty on water undertakers, so far as is reasonably practicable, to ensure that there is, in general, no deterioration in the quality of water which is supplied.

9.2 Water quality changes are occurring all the time and many of these are seasonal or caused by meteorological events or operational processes such as blending, substitution of a groundwater source with a surface water derived supply or the provision of a standby supply. Also, a change in concentration of any substance which does not breach a prescribed maximum or minimum concentration does not in itself necessarily indicate a material deterioration in quality. The Secretaries of State will have regard to these factors in considering any notification of deterioration.

10.1 Applications for relaxation under Regulation 4 should contain the following information:

11.1 Water undertakers are required by Regulation 30(1) to make available to the public the record of water quality inrormation they must maintain under Regulation 29. This record must be available for inspection at all reasonable hours and free of charge at those of their offices which are normally open to the public.

11.2 The intention of this provision is to enable consumers to inspect the record during normal working hours at offices which are within reasonable travelling distance. Water undertakers should keep the appropriate Department informed of the names and addresses of the offices where the record is available for public inspection.

11.3 Water undertakers are required by Regulation 30(4) to provide local authorities with information about the quality of water in their areas at least once a year. This is a minimum requirement. Many water undertakers currently have arrangements with local authorities under which they supply the local authorities with more frequent reports on the quality of water in their areas. Mutually acceptable arrangements of this nature are strongly recommended. Attention is also drawn to the powers available to local authorities under Section 59 of the Act to obtain information on water quality.

The following guidance letters issued by the Department of the Environment and the Welsh Office to water undertakers contain information which is relevant to the provision of wholesome water. A copy of these letters is attached.

WP/1/1986	Asbestos and drinking water	20/2/86
WP/12/1986	Chlorination byproducts in drinking water	4/9/86
WP/4/1987	Guidance for dealing with incidents and emergencies involving the release of radioactivity to the environment	11/5/87
WP/9/1987	Water fluoridation schemes	12/11/87
WP/7/1988	Coal tar pitch particles and polycylic aromatic hydrocarbons in drinking water	1/11/88
WP/2/1989	Products based on polyacrylamide and acrylamide/acrylate copolymers	10/2/89
WP/3/1989	Aluminium in drinking water	13/2/89
WP/5/1989	Epoxy resin lining of water mains	22/3/89
WP/6/1989	Cryptosporidium in water supplies	22/3/89
WP/15/1989	Cryptosporidium in water supplies	29/9/89
WP/17/1989	Lead in water	29/9/89
WP/18/1989	Pesticides in drinking water	29/9/89

1. Medical advice has been sought on possible health risks from asbestos in drinking water. The DHSS Committee on Medical Aspects of the Contamination of Air, Soil and Water has now provided the following statement which will be of interest to water undertakers.

2. A copy of this letter is being sent to the Water Companies' Association for distribution to their members. We are also sending a copy to the Secretary of the Water Authorities' Association; the Chief Engineer, Civil Engineering and Water Services Directorate, Scottish Development Department; the Assistant Secretary, Water Service Division, Department of the Environment for Northern Ireland and the heads of the Land Drainage and Fisheries Divisions of MAFF.

3. Enquiries on this letter should be directed in England to Mr O D Hydes (01-2126359) Water Technical Division, Romney House, 43 Marsham Street, London SWlP 3PY and in Wales to Mr J E Saunders (0222 823178) Water and Environmental Protection Division, Welsh Office, Cathays Park, Cardiff CF1 8NQ.

4. Finally, you will have noticed that this letter has been given a WP index number. This stands for Water Policy and is intended as a more accurate title than the former Water Information. In all other respects WP letters are identical with, and henceforth supersede, Wl letters.

* Conway, D M & Lacey, R F 'Asbestos in Drinking Water' Technical Report TR 202, Water Research Centre, Medmenham, March 1984.

To: Chief Executives of Water Authorities and Secretaries of Water Companies in England and Wales

1. Medical advice has been sought on the possible health risks from chlorination byproducts in drinking water. Over the past 18 months the DHSS Committee on Medical Aspects of Air, Soil and Water has considered the relevant data from the areas of epidemiology, animal carcinogenicity and mutagenicity.

2. The Committee has now provided the attached statement which will be of interest to water undertakers. The Committee's conclusions are restated below:

3. The Committee has also made recommendations for further research associated with mutagenicity assays of concentrated extracts of chlorinated water and these are being explored by the Water Research Centre. It has advised that further research using epidemiological studies and long-term carcinogenicity bioassays is not appropriate at present.

4. When formulating their recommendations the Committee addressed the health risks from chlorination byproducts in drinking water. It was not within their remit to consider methods of water treatment designed to minimise the chlorination byproducts passmg into supply, the advantages these methods might offer and their costs. Some water undertakers seeking to improve the aesthetic quality of the water they supply, to reduce growth of organisms or increase the persistence of disinfectant residual within their distribution systems, are now investigating such methods of treatment. The Department and the Welsh Office are fully in favour of these investigations. They also wish strongly to endorse the view of the Committee that effective disinfection of water supplies is of great importance in maintaining public health.

5. Enquiries on this letter should be directed in England to Mr O D Hydes (01-2126359), Water Technical Division, Romney House, 43 Marsham Street, London SWIP 3PY and in Wales to Mr J E Saunders (0222 823178), Water and Environmental Protection Division, Welsh Office, Cathays Park, Cardiff CF1 3NQ.

6. Copies of this letter and the statement are being sent to the Secretaries of the Water Authorities' Association, and the Water Companies Association; the Chief Engineer, Civil Engineering and Water Services Directorate, Scottish Development Department; the Assistant Secretary, Water Service Division, Department of the Environment for Northern Ireland, the heads of the Land Drainage and Fisheries Divisions of MAFF, and to the Chief Executive, Water Research Centre.

COMMITTEE ON MEDICAL ASPECTS OF THE CONTAMINATION OF AIR,SOIL AND WATER CHLORINATION BYPRODUCTS

1. The disinfection of water by chlorination incidentally involves the reaction of chlorine with organic substances, many of natural origin, which are typically present in source waters. The chemicals which are formed as a result are referred to here as 'chlorination byproducts'; some, such as the trihalomethanes, are well characterised, but there are many others that have still to be identified. The concentration of individual chlorination byproducts found in drinking water varies but is typically of the order of a few parts per thousand million (i.e. micrograms per litre).

2. Some of the individual byproducts of chlorination cause cancers in laboratory animals when administered in large doses over long periods. It is therefore pertinent to ask whether the regular consumption of chlorinated drinking water could increase the risk of cancer in humans by virtue of its content of chlorination byproducts. We have considered the relevant data from the areas of epidemiology, animal carcinogenicity and mutagenicity.

3. A large number of epidemiological studies has been undertaken, mainly in the United States. Most of the studies were based on comparisons of cancer mortality or incidence rates in the populations of contrasted areas where exposure to chlorination byproducts was likely to differ as a consequence of differences in the chemical composition of the source water, or in methods of water treatment, or both. Such geographical comparisons could not adequately take into account differences in socioeconomic status, occupation and personal habits (such as smoking, or diet), all of which have an important effect on the risk of development of cancer; they were therefore more useful for generating than testing hypotheses.

4. Although some of the geographical comparisons suggested possible associations between cancers of various organs and the chlorination of drinking water, there was little consistency between the results of the different studies. The most frequent associations were with cancers of the bladder, colon and rectum and these cancers were therefore the most promising for more detailed study.

5. There has been one series of geographical comparisons within the United Kingdom with some relevance 1.2 In common with many of the studies from the United States, however, the measure of exposure was primarily intended to indicate the degree of contamination of water sources prior to treatment: since the organic compounds present in source waters include the precursors of chorination byproducts, the measure of exposure may provide some indication of the concentration of chlorination byproducts in the treated water supply. These studies found no consistent association between the measure of exposure used and the incidence or mortality for any of the sites of cancer investigated, which included cancers of the bladder, colon and rectum.

6. In contrast to geographical comparisons, studies of the case-control type are able to incorporate estimates of individual exposure to chlorination byproducts, and information on some of the other relevant factors such as socioeconomic status, occupation, smoking and diet. More than a dozen such studies have been undertaken but none in the United Kingdom. Although some have found associations between water chlorination and cancers of various organs, induding the bladder, colon, and rectum, none of the associations is present consistently. In particular, the more recent studies, using detailed intormation from interviews rather than the sparser and probably less accurate data on death certificates, do not confirm the associations suggested by some of the earlier studies.

7. The epidemiological studies do not therefore demonstrate an effect on the risk of cancer to the consumer from chlorination byproducts in drinking water. The uncertainty inherent in the methods at present available for estimating exposures to chlorination byproducts, and the difficulty of interpreting small differences in cancer rates between populations against the usual background variability of such rates, means that risk cannot be totally excluded but also that further epidemiological studies are not likely to lead to substantial clarification.

8. Concentrated organic extracts from chlorinated drinking water have been used in several carcinogenicity studies. Such extracts contain many, but not all, of the organic compounds in the water from which they are derived, their composition depending on the method of extraction.

9. In one of the carcinogenicity studies3, in which groups of rats and mice were given oral doses of concentrated organic extracts from chlorinated drinking water equivalent to at least 100 times the estimated daily intake of drinking water by humans, a dose-related increase in cancers was noted in rats, and a high incidence without a dose response in mice. This study was deficient in several respects, including the lack of suitable control groups of animals, and insufficient details of the pathological findings; cancers of the bladder, colon, or rectum were apparently not increased. None of the other studies, whether using oral administration (e.g. reference 4), subcutaneous injection or cutaneous application of extracts has been shown to cause cancer in the animals exposed.

10. Each of these studies had limitations, and none was an adequate test of the carcinogenicity of the extracts. However, the preparation of sufficient extract to permit a conventional carcinogenicity bioassay of adequate size and duration would be a major undertaking, and the interpretation of the results would be fraught with difficulty in view of the complex and variable composition of the concentrates. We do not therefore, recommend further long term carcinogenicity test of such extracts on whole animals at the present time.

11. The results of mutagenicity tests on a substance are frequently used as an indication of its potential carcinogenicity. Much work has been done using concentrated extracts of chlorinated water in mutagenicity tests. As with the extracts used in the carcinogenicity studies, the composition depends on the method of extraction.

12. Concentrated organic extracts of chlorinated drinking water are strongly mutagenic in bacterial assays and in vitro tests using mammalian cells, but did not produce chromosome damage in mouse bone marrow in an in vivo study. The mutagenicity of the extracts in bacterial tests is typically reduced by the addition of liver microsomal enzymes, and the ability to produce structural chromosome aberrations in cultured mammalian cells is reduced in the presence of blood serum. We therefore consider it unlikely that chlorination byproducts in drinking water would be mutagenic in man following absorption from the gut and transport in the blood to the rest of the body via the liver. This deduction is consistent with the results of the in vivo tests.

13. There remains the theoretical possibility that a direct mutagenic action of chlorination byproducts on the mucosa lining the alimentary tract may lead to cancer. Insofar as the possible associations suggested by the initial epidemiological studies included associations with cancers of the colon and rectum (as noted in paragraph 4) this hypothesis merits further investigation.

14. We recommend that the results of the mutagenicity assays of concentrated extracts of chlorinated water should be explored further, by:

15. We advise that the following lines of research are not justified at present:

16. We have found no sound reason to conclude that the consumption of the byproducts of chlorination, in drinking water which has been treated and chlorinated according to current practices, increases the risk of cancer in humans.

17. The effective disinfection of water supplies is clearly of great importance in maintaining public health. In our opinion, modification of chlorination processes which have proved effective over many years, or the replacement of chlorination by other disinfectants, is not required by the available data on cancer epidemiology, animal carcinogenicity, and mutagenicity in relation to chlorination byproducts in drinking water.

1. Beresford, S. A. A.: The relationship between water quality and health in the London area. Int. J. Epidem. 1981;10: 103-115.

2. Beresford, S. A. A.: Cancer incidence and reuse of drinking water Am. J. Epidemiol. 1983;117: 258-68.

3. Truhaut, R., Gak, J. C., Graillot, C: Recherches sur les risques pouvant resulter de la pollution chimique des eaux d'alimentation- I. Water Research 1979:13: 689-97.

4. Kool, H. J., Kuper, F., van Haerigen, H., Koeman, J. H.: A carcinogenicity study with mutagenic organic concentrates of drinking water in the Netherlands. Fed. Chem. Toxic. 1985; 23: 79-85.

To: Chief Executives of Water Authorities and Secretaries of Water Companies in England and Wales

GUIDANCE FOR DEALING WITH INCIDENTS AND EMERGENCIES INVOLVING THE RELEASE OF RADIOACTIVITY TO THE ENVIRONMENT

Following the accident at Chernobyl, the Government instigated a review of the arrangements for dealing with nuclear emergencies that might affect the UK. This resulted in a report to Ministers and in response to a Parliamentary Question the Prime Minister on 18 December 1986 made a statement, the text of which is annexed to this letter.

These developments prompted the issue of new Guidance as above and we now enclose a copy which supersedes the 'Instructions in the Event of an Accidental Release of Radioactivity' dated December 1983. If you wish to see a copy contact Mr White, Room B454, ext 5486.

Except for Appendix 3 listing establishments for which emergency folders have been prepared, all appendices have been removed from your copy of the Guidance because they concern only Government departments. You will see that the possible contamination of public water supplies by radioactive substances features prominently in the Guidance and we draw your attention particularly to the contents of section 9 (General Advice to Water Authorities) and to section 10 concerning sampling.

Paragraph 10.21 states that a supplement dealing specifically with sampling procedures will be issued shortly. This is currently being prepared by the working group established jointly by the Department, the Water Authorities Association and the Water Companies Association. We expect it to be available in the autumn. The working group is also examining all aspects of existing contingency arrangements and will recommend any necessary improvements. Apart from this, the Guidance will be reviewed regularly by the Department and amendments issued as necessary.

Enquiries on this letter should be directed in England to Mr P D Bell (01-212 5589), Water Technical Division, Romney House, 43 Marsham Street, London SWIP 3PY, and in Wales to Mr J Atkins (0222 823235), Water and Environmental Protection Division, Welsh Office, Cathays Park, Cardiff CF1 3NQ.

Copies of this letter and the enclosures are being sent to the Secretaries of the Water Authorities Association and the Water Companies Association; the Chief Engineer, Civil Engineering and Water Services Directorate, Scottish Development Department; the Assistant Secretary, Water Services Division, Department of the Environment Northern Ireland and the Heads of the Land Drainage and Fisheries Divisions of MAFF.

'The first stage of a thorough review of existing emergency plans and procedures in the light of experience of the Chernobyl accident has now been completed by the Cabinet Office in consultation with the appropriate Government Departments and agencies concerned.

The existing plans are addressed specifically to an accident occurring within the United Kingdom and cover both the emergency procedures at the site and offsite arrangements to protect the public. They continue to provide a valid basis for the response to any nuclear accident in the United Kingdom. However, the Government have decided that planning needs to provide more specifically for the response to a nuclear accident outside the United Kingdom.

Detailed planning is now in hand. Among other things this will need to ensure nationwide monitoring coverage and, in the light of expert assessment of the results of monitoring. for the dissemination of appropriate advice and information to the general public. In the event of any future nuclear accident overseas affecting the United Kingdom the Secretary of State for the Environment will take the lead in co-ordinating Government action.

At the same time, the Government will continue to work with our international partners both in the International Atomic Energy Agency and elsewhere to improve the arrangements for co-ordinated international action. In the meantime, the two recently signed International Atomic Energy Agency sponsored conventions should ensure earlier and more effective notification and dissemination of information than occurred in the case of the Chernobyl accident.

I shall make a further statement when the detailed planning now in hand has been completed and appropriate steps will be taken to make the new arrangements known to the public and to all the authorities concerned'.

This letter gives guidance on the role of water undertakers in fluoridation schemes, and should be read together with the letter of 15 November 1985 which gives advice on the provisions of the Water (Fluoridation) Act 1985.

The Department expects water undertakers to be chiefly concerned with the technical feasibility rather than the principle of fluoridation which is a matter for health authorities to consider. To this end it would be helpful if undertakers made available to regional and district health authorities on request an assessment of the technical feasibility and estimated costs of fluoridation to assist health authorities in deciding whether to make formal applications for a scheme. In determining technical feasibility, undertakers will need to take fully into account any long term proposals or possibilities for transferring water from one area to another, and the statutory limitations on providing fluoridated water outside the area covered by the possible scheme (section 1(6) of the Water (Fluoridation) Act 1985). This may involve explaining to the health authorities which areas it would be feasible to fluoridate without the scheme being endangered by future water supply strategy.

The cost of fluoridation schemes is borne by the health authorities concerned, and all costs incurred by water undertakers on schemes should therefore be recompensed.

In the interests of simplicity the water undertaker should normally deal with the regional health authority on matters affecting a scheme which covers or may cover more than one district health authority area, as the regional authority will be acting as a co-ordinator for the district authorities. Where the regional authority does not take this role, one district wi11 be nominated to take on co-ordination for all the authorities involved.

If the water undertaker agrees in principle to provide a fluoridation scheme in accordance with the application of one or more DHAs, it will need to negotiate the terms of an agreement so that the rights and obligations of each party are clearly understood and the full costs of fluoridation are borne by health authorities. The Model Agreement enclosed with this letter has been prepared by DHSS following discussions with representatives of the water industry and this Department. It sets out the principal items to be taken into account in reaching an agreement and forms a basis for discussion. Variations may be necessary in the light of local conditions or views.

This Code updates and replaces guidance given in the Second Biennial Report of the Standing Technical Advisory Committee on Water Quality published in 1981. Water undertakers should comply with the provisions of this Code. In view of its comprehensive nature the Department will no longer be inspecting and approving fluoridation installations, or requiring information on their performance. Health authorities will make their own arrangements with undertakers about monitoring performance in order to comply with their obligations under section 1(5) of the 1985 Act. The Department will co-ordinate any future revisions of the Code.

The Secretary of State for Social Services will continue to indemnify water undertakers carrying out fluoridation schemes requested by health authorities against legal challenge. The terms of the new indemnity are attached. As the Act provides clear power for water authorities to fluoridate, the indemnity no longer covers this point. It does however indemnify against the unlikely event of any damages awarded in respect of adverse effects on a person's health caused by fluoridation.

Copies of this letter and the attached documents are being sent to the Water Companies' Association for distribution to their members and for information to the Secretary of the Water Authorities Association; the Chief Engineer, Civil Engineering and Water Services Directorates, Scottish Development Department; the head of the Water and Environmental Protection Division, Welsh Office, the Assistant Secretary, Conservation Division, Department of the Environment for Northern Ireland; the heads of the Land Drainage and Fisheries Divisions of Maff, and the head of the Family Practitioner Services Division 2A(1) of DHSS.

Enquiries about this letter, the Model Agreement, and the indemnity may be addressed to C P Douglas, DOE, Room A444, Romney House, 43 Marsham Street, London, SWIP3PY (01-212 6355) and enquiries about the Code of Practice may be addressed to O D Hydes at the same address (01-212 6359).

To: Chief Executives of Water Authorities and Secretaries of Water Companies in England and Wales

1. An advisory limit of 0.2 microgram per litre for the total concentration of six specified polycyclic aromatic hydrocarbons (PAH) was proposed by the World Health Organisation (WHO) in the 1970 European Standards for Drinking Water. In 1980, this limit was incorporated as a standard in the EC Directive relating to the Quality of Water intended for Human Consumption (80/778/EEC) and the standard has been mandatory in the UK since July 1985. It now relates to individual samples following the advice on interpretation of EC Directive standards given in Water Policy Letter WP1/1988 issued on 10 March 1988. A guideline value of 0.01 microgram per litre for benzo [a] pyrene, an Individual PAH, was recommended by WHO in the Guidelines for Drinking Water Quality published in 1984.

2. Advice has been sought from the Department of Health Committee on the Medical Aspects of the Contamination of Air, Soil and Water (CASW) on the possible health risks from coal tar pitch particles (CTPP) and PAH in drinking water. This letter outlines the background to the problem, sets out the medical advice received and gives interim guidance on the monitoring for PAH in drinking water.

3. From the last century to the mid 1970s most water distribution mains made of cast or ductile iron were given an internal anti-corrosion coating of coal tar pitch before being laid in the ground. Coal tar pitch can contain up to 50% of PAH and water supplied through mains lined with coal tar pitch has been found occasionally to contain PAH in solution and in suspension. That in solution arises mainly through leaching from the coating while that in suspension comes from the shedding of particles as a result of deterioration of the coating. Some PAH are known to be carcinogenic in animals and may be carcinogenic in humans. It should be noted that some mains are lined with bitumen which is cxclusively of petroleum or asphalt origin and normally contains very low levels of PAH.

4. A major survey for PAH in water was carried out for the Department of the Environment (DOE) in the mid 1970s by the Water Research Centre (WRc) and was reported in TR 158 published in 1981¹. It was found that PAH concentrations in groundwater sources were extremely low and that any PAH present in surface water sources was removed by coagulation, sedimentation and filtration at treatment works. Most drinking water at consumers' taps contained PAH concentrations well below 0.2 microgram per litre. A few samples exceeded this concentration and it was shown that the PAH consisted almost entirely of fluorathene, a PAH which is not considered to be carcinogenic, derived from the coal tar pitch lining. Since 1977 water undertakers have ceased laying mains coated with coal tar pitch following a recommendation stemming from that survey

		Introduction
Chapter	1	Identification of Water Supply Zones
	2	Identification of Sampling and Supply Points, and Sampling Procedures
	3	Sampling Frequencies
	4	Performance Required of Analytical Systems
	5	Analytical Methods
	6	Analytical Quality Control
	7	Action if Quality Standard Infringed
	8	Action where Risk of Water becoming Unwholesome after leaving Undertakers' Pipes
	9	Deterioration in Quality
	10	Applications for Relaxations
	11	Provision of Information Annex 1 Guidance Letters Annex 2 References

M G HEALEY	L E TAYLOR
Water Technical Division	Water and Environmental Protection Division
Department of the Environment	Welsh Office

DOE/Welsh Office	1 November 1988
WP7/l988

Department of the Environment Welsh Office

Guidance on Safeguarding the Quality of Public Water Supplies

Contents

(Parts IV and V of Regulations)

Sampling from random points

Sampling from fixed points

Sampling for lead, copper and zinc

Sampling for microbiological parameters Consumers' taps

Treated water leaving treatment works

Service reservoirs and water towers

Hydrants, meter boxes and standpipes

Authorisation of supply points

Sampling Procedures

All parameters (except microbiological)

Microbiological parameters

3 Sampling Frequencies

(Regulations 13,17 and 19)

Authorisation of reduced sampling frequencies

Operational sampling

Individual parameters

Timing of sampling

(Regulation 21)

Non-microbiological parameters

Microbiological Parameters

(Part II and Schedule 2 of Regulations)

All parameters (except microbiological)

Microbiological parameters

6 Analytical Quality Control

Non-microbiological parameters

Microbiological parameters

(Part II of Regulations)

Any significant water quality failure

Any standard infringed owing to fittings in ownership of consumer

Microbiological standard infringed

Chemical standard temporarily infringed owing to emergency or operational difficulties

Chemical standard infringed regularly or chronically

Pesticide standard infringed

Standard infringed for other reasons

Emergency procedures

Table 7.2 Advisory Values for some Pesticides*

(Regulation 24)

Lead

9 Interpretation of Deterioration in Quality

10 Applications for Relaxation

(Regulation 4)

11 Provision of Information

(Regulation 30)

ANNEX 1 Guidance Letters

Guidance on Safeguarding the
Quality of Public Water Supplies

Sampling for microbiological parameters
Consumers' taps

Table 7.2 Advisory Values for some Pesticides^*