Archive:
(for archive/historical purposes, this document has not been updated)Index of Contents:
- Introduction
- Bacteria
- Pesticides
- Lead
- Iron and Manganese
- Cryptosporidium
- Drinking Water Quality Incidents
- Determinations in 1998
1. Introduction
The Drinking Water Inspectorate (DWI) checks that water companies supply water that is safe to drink when it reaches your home. This leaflet summarises the results of our checks on Thames Water Utilities Limited during 1998 and should be read in conjunction with DWI's "How Good is the Drinking Water ?" leaflet which is available from us free of charge.
Thames Water continues to supply you with drinking water of a high quality. In 1998, 99.84% of more than 454,200 tests met the standards. This is above the overall figure for England and Wales of 99.78%.
None of the failures in 1998 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 1998 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 during 1998. There had been a significant decrease over the last three years in the number of service reservoirs contravening microbiological standards. The number of bacteriological failures at consumers' taps has remained little chaged at 1.7% of the samples taken. Many of these failures maybe due to the condition of the tap and not the water itself. Most of the contraventions of the microbiological standards were considered not significant or unlikely to recur, but the Inspectorate took action to ensure improvements were made at one works and to supplies from two service reservoirs. The bacteria found were not harmful to consumers' health.
3. Pesticides
Thames Water carried out more than 253,100 tests for individual pesticides during 1998 and all except 12 met the stringent standard. This reflects the significant investment in recent years to install treatment to remove pesticides from drinking water. The Inspectorate took action to ensure that necessary improvements were made to supplies in two zones.
4. Lead
Thames Water had 3 of 1,065 samples taken fail the standard for lead. In all cases the householder was informed of the problem. 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 from us free of charge.
5. Iron and Manganese and polycyclic aromatic hydrocarbons (PAH)
These three parameters provide a good indication of the overall condition of the mains used to distribute drinking water through the region.
No samples failed the standard for manganese during 1998. The number of zones contravening the standard for iron was similar to that over the last three years, while the number of zones failing to meet the standard for PAH has fallen again for the third consecutive year. This overall improvement reflects the impact of the programme of work being carried out by Thames Water to renovate its distribution system. The programme of improvement is ongoing, with Thames Water being required to renovate more than 2,368 km of mains by the end of 2003.
6. Cryptosporidium
Cryptosporidium is a tiny micro-organism which can sometimes cause a form of diarrhoea called cryptosporidiosis. No instances were reported to the Inspectorate of the detection of cryptosporidium in water leaving Thames Water's water treatment works during 1998.
Water companies will shortly be required to sample continuously and analyse daily for cryptosporidium in the treated water at their most vulnerable sites. It will be an offence if they fail to meet a new treatment standard.
7. Drinking Water Quality Incidents
During 1998 nine incidents in which drinking water quality deteriorated were reported to the Inspectorate. The Inspectorate has investigated or will investigate and report on each incident.
Three of the incidents involved the supply of discoloured water to parts of London and followed planned work on the distribution system by the Company in Whitechapel, Blackfriars and Richmond; a further incident was associated with complaints of illness following the supply of discoloured water to part of Thatcham in Berkshire; two incidents involved the detection of coliforms within the distribution system in New Malden and North Streatham; one incident involved loss of supplies and low pressure to parts of Ilford; the remaining two incidents involved complaints from consumers of objectionable tastes or odours in the water supply, the first relating to a petrol-like odour in Mitcham, Surrey and the second to a chlorinous taste in East London.
8. Determinations in 1998
Parameter
Total
Contravening PCV No % Coliforms 19515 325 1.7 Faecal coliforms 19515 13 0.1 Colour 2098 0 0.0 Turbidity 2124 0 0.0 Odour 1214 2 0.2 Taste 1195 1 0.1 Hydrogen ion 2099 0 0.0 Nitrate 2120 2 0.1 Nitrite 6803 193 2.8 Aluminium 2123 0 0.0 Iron 2543 16 0.6 Manganese 2095 0 0.0 Lead 1065 3 0.3 PAH 1284 28 2.2 Trihalomethanes 955 1 0.1 Total pesticides 15006 0 0.0 Atrazine 14526 10 0.1 Diuron 14526 0 0.0 Isoproturon 14526 0 0.0 MCPA 7708 2 < 0.1 Other pesticides 201875 0 0.0 Ammonium 2120 0 0.0 Benzo-3,4-pyrene 1284 2 0.2 Copper 1065 0 0.0 Mercury 259 2 0.8 Oxidisability 236 0 0.0 Potassium 242 1 0.4 Sodium 242 1 0.4 Zinc 1065 0 0.0 All others 37727 0 0.0 Total 378919 602 0.2
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Drinking Water Inspectorate,
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Updated 11 July 2001
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