Archive:
(for archive/historical purposes, these documents have not been updated)Index of Contents:
- Introduction
- Bacteria
- Lead
- Iron and Manganese
- Cryptosporidium
- Drinking Water Quality Incidents
- Prosecution
- Determinations in 1999
1. Introduction
The Drinking Water Inspectorate (DWI) checks that water companies supply water that is safe to drink when it reaches your home. This document summarises the results of our checks on Thames Water Utilities Limited during 1999 and should be read in conjunction with DWI's "How Good is the Drinking Water?" leaflet which is available here and also from us free of charge from the address at the end of this document.
Thames Water continues to supply you with drinking water of a high quality. In 1999, 99.87% of more than 452,500 tests met the standards. This is above the overall figure for England and Wales of 99.82%.
None of the failures in 1999 were likely to harm consumers' health. We assessed each one and, where necessary, we have required Thames Water to take action to prevent further failures.
Although the 1999 results are good, we know that there are some matters of everyday concern to consumers. These are detailed below including the steps taken by Thames Water to further improve its performance.
2. Bacteria
Whenever bacteria are found in water samples Thames Water investigates immediately.
Occasionally low numbers of bacteria were detected in the water leaving a small number of water treatment works and service reservoirs during 1999. The number of bacteriological failures at consumers' taps was 1.2% of the samples taken. Some of these failures may be due to the condition of the tap and not the water itself. The bacteria found were not harmful to consumers' health.
The Inspectorate required action to be taken to secure improvements at three treatment works, at two service reservoirs, and in one water supply zone.
3. Lead
Samples occasionally fail the standard for lead, even where additional treatment has been installed to reduce the amount of lead picked up by water from pipework. In many cases this is due to the consumer's water pipes being made of lead. In all cases the householder has been informed of things they can do to reduce lead levels at their tap. The Drinking Water Inspectorate advises consumers living in properties with lead pipes to seek advice from their water company. A DWI leaflet about lead in drinking water is also available here and from us free of charge from the address at the end of this document.
4. Iron and Manganese
One sample from 2,127 taken failed the standard for manganese during 1999. The number of zones contravening the standard for iron has been slowly reducing in recent years. This reflects the impact of the programme of work being carried out by Thames Water to renovate its distribution system. The programme is ongoing, with Thames Water being required to renovate more than 3,500km of mains from 1999 to 2003.
These parameters provide a good indication of the overall condition of the mains used to distribute drinking water through the region.
5. Cryptosporidium
Cryptosporidium is a tiny micro-organism that can sometimes cause a form of diarrhoea called cryptosporidiosis. There are a number of sources of Cryptosporidium other than water but due to new regulations water companies are now required by law to sample continuously and analyse daily for Cryptosporidium in the treated water at those sites which have a potential vulnerability. All water companies had to initially conduct risk assessments at their sites to identify if there was any significant risk of contamination. Thames Water identified that there was significant risk at 21 of its sites and it has made or is making arrangements for continuously sampling and monitoring the treated water at each of these sites. At all these sites, the Company is required to ensure adequate treatment is in place and it is an offence if the new treatment standard for Cryptosporidium is exceeded. In addition to the regulatory requirement, the Company is able to get early warning of any treatment problems from this monitoring system.
6. Drinking Water Quality Incidents
During 1999, 13 incidents in which drinking water quality deteriorated were reported to the Inspectorate.
Eleven of the incidents involved the supply of discoloured water to consumers. In three cases, at Blunsden (twice) and North Orpington, the discolouration arose as a result of burst mains in the distribution system, or following measures to maintain supplies following a burst main. In the other eight cases, at Putney, Milford, Peckham/Dulwich, Tadley, Earley, Hammersmith, Swindon and Beckenham, discolouration occurred following work carried out by the Company on the distribution system. The remaining two incidents concerned the loss of disinfection at Pangbourne water treatment works and the detection of low level microbiological contamination at Goose Green water tower and surrounding properties in the Hoddesdon area.
7. Prosecution
During a refurbishment of a main that supplies properties in Ewhurst, Surrey, in 1997, mains were initially allowed to drain down causing a loss of supply. In 48 hours the direction of the flow of water through the village changed a number of times, the reversals causing a supply of discoloured water to a large part of the villiage.
Following investigation by the Inspectorate, on 26 January 2000 at Guildford Magistrates Court Thames Water pleaded guilty to four offences of supplying water unfit for human consumption. The Company was fined a total of £12,000 with £3,900 costs.
8. Determinations in 1999
Parameter
Total
Contravening PCV No % Coliforms 19689 236 1.2 Faecal coliforms 19689 10 0.1 Colour 2137 0 0.0 Turbidity 2170 1 < 0.1 Odour 1207 4 0.3 Taste 1193 3 0.3 Hydrogen ion 2133 0 0.0 Nitrate 2173 2 0.1 Nitrite 6898 154 2.2 Aluminium 2125 0 0.0 Iron 2527 10 0.4 Manganese 2127 1 < 0.1 Lead 1086 3 0.3 PAH 1202 38 3.2 Trihalomethanes 985 0 0.0 Total pesticides 14288 0 0.0 Atrazine 14327 16 0.1 MCPA 7554 0 0.0 Other pesticides 226918 0 0.0 Ammonium 2128 0 0.0 Benzo-3,4-pyrene 1202 2 0.2 Mercury 265 0 0.0 Nickel 248 1 0.4 Potassium 253 0 0.0 Sodium 253 0 0.0 Surfactant 258 1 0.4 All others 39989 0 0.0 Total 375024 482 0.1
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Drinking Water Inspectorate,
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Telephone : 020 7944 5956 - Facsimile : 020 7944 5969
E-mail: dwi_enquiries@detr.gov.uk
Published 12 July 2000 / Updated 11 July 2001
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