Chief Inspector's Report 2002
Part 1
Overview of Water Quality in England and Wales
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Summary Information
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Introduction
Overview Format
This part of the report provides a summary of the overall quality of drinking water supplied during 2002 to over 52 million consumers in England and Wales.
The Overview Chapter is split into five general sections as follows:
- Overall Water Quality in 2002 - 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 2002, compared with previous years.
- 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 2002 is presented in table form. Comparative data from 2001 and 2000 have also been included.
Where information concerning overall compliance or numbers of non-compliant 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 non-compliance, in water supply zones, in 2002 is shown in the form of a pie chart.
Overall Water Quality in 2002
At water treatment works, in service reservoirs and in water supply zones, the 26 companies carried out a total of 2,973,561 tests in 2002. Of these, 99.87% demonstrated compliance with the relevant water quality standards. This compares with 99.86% for 2001, with the number of samples breaching the standard reducing from 4,054 in 2001 to 3,741 in 2002.
The overall number of tests failing the standards has decreased from 36,806 in 1993 to 3,741 in 2002. This represents a reduction of 93% over the last ten years.
Coliforms were absent from samples taken from 1,230 (91.52%) of the 1,344 sampling points at water treatment works.
Total coliforms were absent from at least 95% of samples (the regulatory standard) taken from 4,678 (99.72%) of the 4,693 sampling points at service reservoirs.
Figure 1 below shows the overall compliance with the standards, specified in the Water Quality (Water Supply) Regulations 1989, over the last ten years. The improvement is best seen in Figure 2, which shows the decreasing number of breaches of the standards.
The improvement since 1993 is mainly due to significant reductions in the number of breaches of the total coliform and faecal coliform standards at water treatment works and in service reservoirs, and, in 2002, of the iron, turbidity, nitrate and lead standards in zones.
Figure 1 - Overall Compliance with Regulatory Standards
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Figure 2 - Total Number of Breaches of Numerical Standards
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Microbiological Quality of Water Leaving Treatment Works
Table 1 below shows the companies' performance in 2002, with data for 2001 and 2000 for comparison.
Table 1 Microbiological Quality of Water Leaving Treatment Works
| 20021 | 2001 | 2000 | |
| Number of water treatment works | 1,344 | 1,386 | 1,388 |
| COLIFORMS | |||
| Total number of tests | 163,756 | 164,429 | 173,544 |
| - number containing coliforms | 145 | 169 | 247 |
| - % containing coliforms | 0.09 | 0.10 | 0.14 |
| Treatment works with coliforms detected | 114 | 133 | 182 |
| - % of all works | 8.48 | 9.60 | 13.11 |
| FAECAL COLIFORMS | |||
| Total number of tests | 163,779 | 164,462 | 173,533 |
| - number containing faecal coliforms | 20 | 30 | 43 |
| - % containing faecal coliforms | 0.01 | 0.02 | 0.02 |
| Treatment works with faecal coliforms detected | 19 | 28 | 41 |
| - % of all works with faecal coliforms detected | 1.41 | 2.02 | 2.95 |
Figures 3 and 4 below show the companies' performance in meeting the regulatory requirements at water treatment works over the last ten years.
In Figure 3, overall compliance with the regulatory requirements since 1993 is shown. Figure 4 shows the trend in the proportion of treatment works at which coliforms or faecal coliforms have been detected over the last ten years.
Figure 3 - Microbiological Parameters at Water Treatment Works
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Figure 4 - Microbiological Parameters at Water Treatment Works
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There has been a further decrease, since 2001, in the number of treatment works, and samples from treatment works, where both total and faecal coliforms were detected.
A total of 145 samples taken from 114 treatment works (8.48% of all works) were found to contain total coliforms, compared with 169 samples from 133 treatment works (9.60%) in 2001. Faecal coliforms were detected in 20 samples taken from 19 treatment works (1.41% of all works), compared with 30 samples from 28 treatment works (2.02%) in 2001.
The decrease generally follows the overall ten-year trend, which has seen continued improvement in water quality leaving treatment works. At 99.95%, the overall compliance at treatment works is higher than in any other year.
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.
During 2002, on every occasion total coliforms and faecal coliforms were found, the water companies concerned carried out investigations to determine the nature of the problem. In the vast majority of cases, the Inspectorate considered the breaches of the standards to be either trivial, or unlikely to recur as a result of prompt remedial actions taken by the companies. However, the Inspectorate has considered, or has taken, enforcement action against two companies in respect of breaches of the total coliform standard at seven treatment works. This action will require the companies concerned to take necessary measures to prevent further breaches.
Microbiological Quality of Water in Service Reservoirs
Table 2 below shows the companies' performance in 2002, with data for 2001 and 2000 for comparison.
Table 2 - Microbiological Quality of Water in Service Reservoirs
| 2002 | 2001 | 2000 | |
| Number of water treatment works | 4,691 | 4,746 | 4,782 |
| COLIFORMS | |||
| - number containing coliforms | 367 | 445 | 507 |
| - % containing coliforms | 0.15 | 0.18 | 0.21 |
| Service reservoirs with coliforms detected | 288 | 400 | 427 |
| Service reservoirs with coliforms detected in | |||
| more than 5% of samples | 13 | 6 | 18 |
| - % of all reservoirs with coliforms detected | 0.28 | 0.13 | 0.40 |
| FAECAL COLIFORMS | |||
| Total number of tests | 243,315 | 245,158 | 246,174 |
| - number containing faecal coliforms | 57 | 62 | 81 |
| - % containing faecal coliforms | 0.02 | 0.03 | 0.03 |
| Service reservoirs with faecal coliforms detected | 56 | 58 | 72 |
| - % of all service reservoirs with faecal | |||
| coliforms detected | 1.19 | 1.22 | 1.51 |
Figures 5 and 6 below show the companies' performance in meeting the regulatory requirements at service reservoirs over the last ten years.
In Figure 5, overall compliance with the numerical standards for coliforms and faecal coliforms since 1993 is shown. Figure 6 shows the trend in the proportion of service reservoirs breaching the standards for coliforms or faecal coliforms over the last ten years.
It should be noted that, whilst Figure 6 shows the proportion of service reservoirs where coliforms were absent from at least 95% of samples taken over the year (the regulatory standard), all incidences of detections of coliforms have been used in generating Figure 5.
Figure 5 - Overall Compliance with Standards for Microbiological Parameters at Service Reservoirs
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Figure 6 - Service Reservoirs Breaching Standars for Microbiological Parameters
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In 2002 there was a decrease in the number of service reservoirs, and samples from service reservoirs, containing total coliforms and faecal coliforms. However, the number of service reservoirs breaching the regulatory standard for total coliforms increased. In 2002, 13 (0.28%) of the 4,691 service reservoirs relating to seven water companies failed to comply fully with the standard compared with six (0.13%) service reservoirs relating to four companies failing the standard in 2001. This increase is not statistically significant.
The number of service reservoirs failing to comply with the standard for faecal coliforms decreased slightly from 58 (1.20%) in 2001 to 56 (1.19%) in 2002.
During 2002, a total of 486,601 microbiological tests were carried out on samples taken from service reservoirs. Total coliforms or faecal coliforms were detected on 424 occasions, giving an overall compliance figure of 99.91%, an improvement on the figure of 99.90% for 2001.
On each occasion that the standards for total coliforms or faecal coliforms were breached, the companies carried out an investigation into the cause and, where necessary, took appropriate remedial action. In the majority of cases, the Inspectorate considered the breaches to be either trivial, or unlikely to recur because of the actions taken. However, enforcement action has been taken, or is under consideration, for breaches of the faecal coliform standard at one service reservoir.
Water Quality in Water Supply Zones
Table 3 below shows the companies' performance in 2002, with data for 2001 and 2000 for comparison.
Table 3 - Water Quality in Water Supply Zones
| Parameter | Total numberof tests takenin 2002 |
Tests not meeting |
Number of zones not complying with
the standards |
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Number |
% |
2002 |
2001 |
2000 |
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| Coliforms | 149,385 |
784 |
0.53 |
12 |
5 |
8 |
| Faecal coliforms | 149,393 |
59 |
0.04 |
59 |
60 |
60 |
| Colour | 41,813 |
2 |
<0.01 |
2 |
2 |
8 |
| Turbidity | 58,709 |
25 |
0.04 |
23 |
42 |
33 |
| Odour | 14,964 |
6 |
0.04 |
6 |
5 |
6 |
| Taste | 14,916 |
3 |
0.02 |
3 |
2 |
5 |
| Hydrogen ion | 57,437 |
11 |
0.02 |
10 |
8 |
27 |
| Nitrate | 34,954 |
38 |
0.11 |
15 |
26 |
10 |
| Nitrite | 32,255 |
1,022 |
3.17 |
131 |
149 |
184 |
| Aluminium | 37,187 |
26 |
0.07 |
23 |
27 |
35 |
| Iron | 53,239 |
442 |
0.83 |
307 |
345 |
375 |
| Manganese | 40,621 |
102 |
0.25 |
84 |
94 |
97 |
| Lead | 20,682 |
87 |
0.42 |
80 |
105 |
135 |
| PAH | 11,258 |
337 |
2.99 |
185 |
168 |
174 |
| Trihalomethanes | 11,710 |
93 |
0.79 |
15 |
35 |
45 |
| Total pesticides | 47,414 |
6 |
0.01 |
6 |
4 |
1 |
| Individual pesticides | 856,513 |
66 |
0.01 |
59 |
70 |
44 |
| All others | 479,918 |
43 |
0.01 |
29 |
49 |
28 |
| TOTAL | 2,112,368 |
3,152 |
0.15% |
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- |
- |
2,284 zones in 2002; 2,306 zones in 2001; 2,316 zones in 2000
Figure 7 below shows the overall compliance with water quality standards in companies' water supply zones over the last ten years.
The 'compliance figures' in this chart have been derived by taking the total number of tests in zones and the number of occasions on which one or more sample has breached the relevant numerical standard ('point breaches'). This does not take into account parameters such as total coliforms where compliance is based on 95% of samples, or certain other parameters where compliance with the standard is based on an average of results. The data is, however, considered a useful indicator of the trend in water quality in supply zones over the last ten years.
Figure 7 - Overall Compliance with Standards in Water Supply Zones
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Since 1993, there has been a reduction in the number of test results from zones which failed to comply with the relevant standards. In 2002, only 3,152 (0.15%) of the 2,112,368 tests carried out in zones failed to comply fully with the standards, compared with 34,784 (1.38%) of 2,529,485 samples failing in 1993.
Trends over the last ten years in compliance with the standards for the 55 individual parameters which have a numerical standard, and which companies must test for in all of their water quality zones, are represented in the following six charts (Figures 8 to 13). In this case the percentage figures are calculated from data for zonal compliance and therefore do take account of cases where compliance is based on a percentage, or on average results.
For clarity, the parameters have been arranged in groups of broadly similar character, and the charts below generated according to these groups, but it should be stressed that these groupings do not have any scientific or regulatory significance. The groups are categorised as follows.
- Microbiological Parameters: namely total and faecal coliforms;
- 'Physical' Parameters: parameters which, in general terms, affect the appearance, taste or odour of the water;
- 'Metals' Parameters: trace metals, such as iron or lead, which may be detected in drinking water;
- 'Organic' Parameters: parameters such as pesticides, and disinfection by-products which companies regularly monitor for;
- 'Ionic' Parameters: pH, nitrate and nitrite;
- All Other Parameters: a combined figure for the remaining 38 parameters, regularly tested for but rarely found at non-compliant levels.
For further information on a specific parameter, please refer to the Quality Standards Table in the introduction to Part 2 of this report.
Figure 8 - Microbiological Parameters
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Figure 9 'Aesthetic' Parameters
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Figure 10 - 'Metals' parameters
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Figure 11 - 'Ionic' Parameters
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Figure 12 - 'Organic' Parameters
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Figure 13 - All Other Parameters
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Non-Compliant Zones
A zone may be non-compliant 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 is being remedied through an undertaking 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 seven parameters in 16 (0.70%) 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 2002. Each is shown as a percentage of the 3,152 individual breaches in water supply zones. A commentary on significant parameters is given below.
Figure 14 - Contraventions of Standards in Water Supply Zones in 2002
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Microbiological Parameters
The number of zones breaching the total coliform standard has shown a slight increase since last year. The increase is not statistically significant and the number of non-compliant zones remains lower than in the years preceding 1999. The number of zones breaching the faecal coliform standard is slightly less than last year.
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 requires 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 2002. A total of 307 (13.32%) zones failed to comply with the iron standard in 2002 compared with 345 (14.97%) zones in 2001.
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 1993 in the number of zones not complying with the lead standard. A total of 80 (3.47%) zones failed to comply with the standard for lead in 2002 compared with 1993, when 538 (20.89%) 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 current standard for lead is 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 20001. 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 decrease since last year. The decrease is not statistically significant but has resulted in the lowest level of non-compliance to date. However, with 1,022 individual tests found to contain nitrite above the standard, it was the most commonly failing parameter.
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. Since 1993, the number of zones not complying with the standard has decreased from 245 (9.51%) to 131 (5.68%). 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.
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, in both 2001 and 2002 the number of zones not complying has increased again. In 2002, 185 (8.03%) zones failed to comply with the PAH standard compared with 147 (6.40%) in 2000. This increase is not statistically significant.
PAH is derived from the distribution system and is often a localised problem. Breaches of the standard in a zone does not mean that the entire water supply in that zone is non-compliant. 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 non-trivial 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. Water distribution undertakings have been adjusted accordingly to give priority to breaches of other standards.
Pesticides (Individual and Total)
During 2002, ten individual pesticides were detected above 0.1µg/l in 53,812 samples. 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 decrease in the number of zones breaching the individual pesticide standard. In 2002, 59 (2.56%) breached the standard compared with 70 (3.04%) in 2001.
Compliance with the pesticide standards remains significantly higher than in 1993.
Turbidity
There has been a significant decrease in the number of zones failing to meet the turbidity standard compared with last year. In 2002, 23 (1.00%) zones breached the standard compared with 42 (1.82%) in 2001.
Manganese
The number of zones failing to meet the manganese standard has decreased. In 2002, 84 (3.64%) zones failed to comply with the standard compared with 94 (4.08%) zones in 2001.The majority of the breaches occurred in zones covered by undertakings.
Other parameters
In 2002, all zones complied with the Regulations in respect of 25 of the other 38 parameters with numerical standards. The standards for a further 13 parameters were breached on only a few occasions in a small number of zones.
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.
1 The Water Supply (Water Quality) Regulations 2001 in Wales
