Overview format

This part of the Report provides a summary of the overall quality of drinking water supplied during 2003 to more than 53 million consumers in England and Wales.

The chapter is split into five general sections as follows:

 

Overall water quality in 2003 – gives summary statistics on water supply information in England and Wales; levels of overall compliance with regulatory standards; and a brief comparison with previous years.

 

Microbiological quality of water leaving treatment works – expands on the information in the overall water quality section and provides further data and analysis on the compliance with standards for water leaving water treatment works in 2003, compared with previous years.

 

Number of water companies*: Number of consumers supplied: Amount of water supplied: Proportion from surface water sources: Proportion from groundwater sources: Number of treatment works: Number of service reservoirs: Number of water supply zones: Total length of mains:

53.3 million15,999 Ml/d 67% 33% 1,303 4,669 2,249 331,338 km

 

Microbiological quality of water in service reservoirs – expands on the information in the overall water quality section and provides additional data and analysis on the compliance with standards that apply to water in service reservoirs, compared with previous years.

 

Water quality in water supply zones – provides greater detail on compliance with the standards for microbiological parameters, and for the 55 parameters with numerical standards that relate to the quality of the water supplied at consumers’ taps.

 

Comparisons of drinking water quality between companies – gives a statistical comparison, using the Overall Quality Index and the Operational Performance Index, of compliance data between different water companies.

 

Statistical significance

Throughout this report, and particularly in this section, the term ‘statistically significant’ is commonly used where comparisons are made between data from different years. Often, apparent differences in the proportion of samples breaching the standards are affected by factors other than water quality, such as differences in the overall number of tests carried out, or changes to the total number of treatment works, service reservoirs or zones. Also, as the number of tests carried out is often very large and the number of breaches of the standards comparatively small, in many cases the differences are sufficiently small to be attributable to random variations.

Therefore in each case, ‘significance’ has been tested using accepted statistical techniques (normal approximation to the binomial distribution; 95% confidence interval) to determine those cases where statistically significant differences can be said to have occurred.

Where changes have been found to be ‘not statistically significantly different’, it indicates that, whilst the numbers may be different, no strong conclusions can be drawn concerning trends.

Presentation of data

For each of the sections dealing with treatment works, service reservoirs and water supply zones, data for 2003 are presented in table form. Comparative data from 2002 and 2001 have also been included.

Where information concerning overall compliance or numbers of noncompliant samples is shown, histograms have been used to represent the data for each year. In cases of individual parameters, line charts have been used as they are considered to be the most effective form to show the trends in compliance with standards over the last ten years. The contributions of individual parameters to the overall level of noncompliance in water supply zones in 2003, are shown in the form of a pie chart.

Figure 3 – Microbiological parameters at water treatment works

Figure 4 – Microbiological Parameters at Water Treatment Works

There has been an increase, since 2002, in the number of treatment works, and samples from treatment works, where both total and faecal coliforms were detected. However, this increase is not statistically significant.

A total of 155 samples taken from 120 treatment works (9.21% of all works) was found to contain total coliforms, compared with 145 samples from 114 treatment works (8.48%) in 2002. Faecal coliforms were detected in 27 samples taken from 25 treatment works (1.92% of all works), compared to 20 samples from 19 treatment works (1.41%) in 2002.

Total and faecal coliforms are not usually considered harmful to health, but they may indicate that more dangerous organisms may be present. Coliform bacteria are easy to detect, and their presence in water leaving a treatment works can indicate that the effectiveness of the treatment or disinfection processes has been compromised. Whenever total coliforms and faecal coliforms are found, the water companies concerned carry out investigations to determine the nature of the problem.

In the vast majority of cases, for 2003, the Inspectorate considered the breaches of the standard to be either trivial, or unlikely to recur, as a result of prompt remedial actions taken by the companies.

The increase in number of treatment works and in samples from treatment works, where total and faecal coliforms were detected, does not follow the tenyear trend seen in previous years, which have seen continued improvement in water quality leaving treatment works. Additionally, the increase is the result of an increase in breaches of total and faecal coliforms standards at the treatment works of one company. The Inspectorate has taken enforcement action against that company, which will require the company to take necessary measures to prevent further breaches.

A zone may be noncompliant because a single result has breached a standard. Some of these breaches have been regarded as trivial in the compliance assessment and do not indicate a serious problem with water quality.

In other cases, a breach of a standard, although not trivial, is considered unlikely to recur as a result of prompt remedial action taken by the company, or an undertaking being given by the company to carry out appropriate work as part of an improvement programme.

Enforcement action has been considered in a small number of cases, where the contravention is likely to recur and where no remedial action is in place. Such action has been considered, or is under consideration, for breaches of standards for five parameters in 12 (0.53%) water supply zones. Full details of this enforcement action are given in Part 3, Section E, of this Report, and in individual company sections.

Figure 14 below shows those parameters for which breaches of standards have occurred in 2003. Each is shown as a percentage of the 2,958 individual breaches in water supply zones. A commentary on significant parameters is given below.

Figure 14 – Contraventions of Standards in Water Supply Zones in 2003

Microbiological parameters

The number of zones breaching the total coliform standard has decreased to 8 (0.35%) in 2003, from 12 (0.53%) in 2002. The number of zones breaching the faecal coliform standard has also decreased to 44 (2.00%) in 2003, from 59 (2.58%) in 2002.

Breaches of the standards in samples taken from consumers’ taps can sometimes be caused by the condition of the plumbing and therefore do not necessarily reflect fully the microbiological quality of the water supplied. However, companies are expected to take appropriate action in the event of any breach of the microbiological standards. The Inspectorate would require evidence, including repeat sampling and sampling from related points, before accepting that the condition of a consumer's tap may be responsible for the breach.

A small number of zones breaching the microbiological standards are already covered by undertakings. For the remainder, the Inspectorate is ensuring that appropriate steps are taken by the companies to restore compliance with the standard.

Iron

There has been a decrease in the number of water supply zones failing to comply with the iron standard during 2003. A total of 259 (11.52%) zones failed to comply with the iron standard in 2003, compared to 308 (13.49%) zones in 2002.

Iron can affect the taste and appearance of the water, and give cause for concern. However, there are no health risks associated with the breaches of the iron standard. Many of the breaches are the result of localised problems within the distribution system, especially where there are unlined cast iron mains. In a few cases the breaches are due to inadequate removal of iron at a treatment works.

Nearly all the breaches occurred in zones covered by undertakings. These undertakings have been given by the companies to carry out improvements in the distribution system or at treatment works. The steady underlying trend of improving compliance with the iron standard can be attributed to the work being carried out under these undertakings. These improvements should continue as the programmes of work are progressed.

Lead

There has been a steady decrease since 1994 in the number of zones not complying with the lead standard. A total of 50 (2.22%) zones failed to comply with the standard for lead in 2003, compared to 1994, when 506 (19.83%) zones failed to comply.

This continued improvement largely reflects the additional treatment that companies have installed, or are installing, under the terms of their undertakings in respect of lead. Such treatment makes the water less able to dissolve lead from pipework, i.e. makes it less plumbosolvent.

The main sources of lead in drinking water are lead service pipes, i.e. the connection from the water main to the property, or internal lead plumbing, which may be present in older buildings. Occasionally, the use of lead solder can cause problems. When considering breaches of the lead standard, it is particularly important to bear in mind that the nature and condition of the pipework at the sampling location may greatly influence the outcome. The detection of lead in samples taken from a particular zone does not necessarily mean that the water is plumbosolvent or that samples from other properties in the zone will fail the standard. As long as lead continues to be present in household plumbing it is likely that occasional breaches of the lead standard will occur in water at consumers' taps.

The standard in place during 2003 for lead was 50 µg/l. The new Drinking Water Directive sets a more stringent interim standard for lead of 25 µg/l, to be achieved by the end of 2003, and a final standard of 10 µg/l, to be met by the end of 2013. These changes to the standard have been incorporated into the new Water Supply (Water Quality) Regulations 2000*. Where necessary, companies have strategies and legally binding programmes of work for achieving compliance with these tighter standards.

Nitrite

The number of zones contravening the standard for nitrite has shown a slight increase since last year. However, the number of individual samples found to contain nitrite above the standard has decreased from 1,022 (3.17%) in 2002, to 950 (2.79%) in 2003.

Detection of nitrite above the current standard of 0.1 mg/l is usually associated with the use of chloramination. In this process, a small amount of ammonia is added after final chlorination to produce a chloramine residual in the water entering the distribution system. The benefits of the process are a longer lasting residual disinfectant in the distribution system, and a reduction in consumer complaints of chlorine taste or odour. The principal disadvantage is that chloramines can break down under certain conditions to form nitrite.

Where chloramination is used, companies have to optimise the process to minimise the risk of nitrite production. As with all parameters, there is a wide margin of safety between the standard and the concentration that is considered potentially harmful to health.

The new EC Drinking Water Directive contains a revised combined standard for nitrite and nitrate, which is based on a formula and recognises the relationship between the two parameters. The Directive also introduces a separate individual nitrite standard which applies at the treatment works, rather than in water supply zones, to take account of the use of chloramine. These changes have been incorporated into the new Water Supply (Water Quality) Regulations 2000* which implement the Directive.

* The Water Supply (Water Quality) Regulations 2001 in Wales

Polycyclic Aromatic Hydrocarbons (PAH)

A steady rise in the number of zones not complying with the standard for PAH was apparent from 1991 to 1996. This trend was reversed in 1997 and a downward trend occurred until 2000. This reflected the programmes of work being carried out as part of the companies’ distribution system undertaking. However, since 2001, the number of zones not complying has increased again. In 2003, 200 (8.89%) zones failed to comply with the PAH standard, compared to 147 (6.4%) in 2000.

PAH is derived from the distribution system and is often a localised problem. A failure of the standard in a zone does not mean that the entire water supply in that zone is noncompliant. The short term remedial measures taken by water companies to alleviate acute water quality problems, such as discolouration, may give rise to breaches of the PAH standard. The distribution undertakings require companies to take account of nontrivial breaches of the PAH standard when assessing priorities for mains renovation.

Although all PAH breaches are investigated, detailed examination of the results shows that, in almost all cases, the contravention of the standard has been caused by only one of the six indicator substances determined in the definition of PAH, namely fluoranthene. The new EC Drinking Water Directive no longer includes fluoranthene as an indicator substance in the PAH standard and this has been taken into account during the making of the new Regulations to implement the Directive. In fact, 335 (99.11%) of the 338 breaches of the ‘old’ standard in 2003 would meet the new standard which came into force 1 January 2004.

Pesticides (Individual and Total)

During 2003, eight individual pesticides were detected above 0.1µg/l in 31 (<0.01%) samples compared to ten individual pesticides in 66 (0.01%) samples in 2002. In every instance the concentrations found corresponded to exposures far smaller than those known to be harmful or likely to affect health.

There has been a significant decrease in the number of zones breaching the individual pesticide standard. In 2003, 26 (1.16%) breached the standard, compared with 59 (2.56%) in 2002.

Turbidity

There has been a slight increase in the number of zones failing to meet the turbidity standard compared with last year. However, this increase is not significant and compared to ten years ago, compliance with the turbidity standard remains high.

In 2003, 31 (1.38%) zones breached the standard, compared with 23 (1.00%) in 2002.

Manganese

The number of zones failing to meet the manganese standard has slightly decreased. In 2003, 78 (3.47%) zones failed to comply with the standard, compared to 84 (3.64%) zones in 2002.The majority of the breaches occurred in zones covered by undertakings.

Other parameters

The number of zones failing to comply with the Regulations in respect of the other 38 parameters with numerical standards increased to 100 (4.45%) in 2003, from 30 (1.3%) in 2002. This increase is mainly due to an increase in the number of breaches of the phosphorus standard for a few water companies where intermittent poor control of phosphate dosing to reduce the levels of lead in water has occurred. The Inspectorate will be investigating the problem with the water companies concerned. However, it is worth noting that the standard for phosphorous no longer applies following the introduction of the new Regulations.

Summary Information

Table 4 below provides a summary of the key information for each of the 26 water companies, listed alphabetically.

It is not designed to make any direct comparisons between companies. The issue of comparison is covered in the next section.

Table 4 – Summary of Key Information

Consumers Water Number of Number of Number Failures for Failures Failures of Failures Failures Failures Total Total %

Comparisons of Drinking Water Quality between Companies

Consumers and organisations frequently ask the Inspectorate how drinking water quality varies from water company to water company.

The Regulations cover 55 parameters with numerical standards, some of which are more important than others in respect of public health and aesthetic considerations. Also, companies vary considerably in size, supplying anywhere between 300 and 7.5 million consumers.

Furthermore, drinking water quality in all water companies is very high with the overall percentage of tests complying with the standards approaching 100%. Meaningful comparisons have to be able to detect small differences in compliance between companies that are statistically significant and have not occurred by chance.

To allow a meaningful comparison to be made, the Inspectorate publishes, for each company, an overall quality index, based on 15 key parameters, and an operational performance index based on six of those key parameters: iron, manganese, aluminium, turbidity, faecal coliforms and trihalomethanes.

It is important to note that the simple percentage of tests complying is a different measure from the overall quality and operational performance indexes. These different measures must not be confused with on e another, as they are not directly comparable.

Overall Quality Index

Table 5 lists the water companies in decreasing order of overall quality index for the calendar year 2003 in three columns; statistically significantly below average, not statistically significantly different from average; and statistically significantly above average. It should be noted that for the smaller water companies with relatively low numbers of samples it is not possible to show whether their index is statistically significantly different from average.

Trends in the overall quality index over the calendar years 1996 to 2003 inclusive have been assessed to determine whether there is a significantly improving trend, no statistically significant trend or a significantly deteriorating trend. Table 6 shows that there were no companies with a significantly deteriorating trend and for five companies Anglian, South Staffordshire, Thames, Dwˆ r Cymru and South West with a significantly improving trend. All other companies showed no significant trend. Five companies – Essex & Suffolk, Northumbrian, United Utilities, Severn Trent and Yorkshire show statistically significant differences between years.

Table 6 – Trend in Overall Quality Index for 1996 to 2003

 

Operational Performance Index

Table 7 lists the water companies in decreasing order of operational performance index for the calendar year 2003 in three columns in a similar manner to the overall quality index.

Table 7 – Operational Performance Index: 2003

Table 8 shows the trend in the operational performance index over the calendar years 1996 to 2003 inclusive. No company shows a significantly deteriorating trend and there is a significantly improving trend for four companies, shown below. Again, all other companies showed no significant trend. Three companies – Northumbrian, United Utilities and Yorkshire show statistically significant differences between years.

Table 8 – Trend in Operational Performance Index for 1996 to 2003