Index of Contents:
- Introduction
- Coliform Bacteria
- Pesticides
- Lead
- Iron and Manganese
- Cryptosporidium
- Drinking Water Quality Incidents
- Further Information
1. Introduction
The Drinking Water Inspectorate (DWI) checks on behalf of the Government that water companies supply water that is safe to drink. This leaflet summarises the results of our checks on Thames Water Utilities Limited during 2001. You should read it alongside DWI’s leaflet, How Good is the Drinking Water? which gives more details on the standards and tests. This is available free of charge and on the DWI web site at www.dwi.gov.uk..
Thames Water continues to supply you with drinking water of a high quality. In 2001, 99.91% of more than 484,600 tests met the drinking water standards. This is above the overall figure for England and Wales of 99.86%. The tests are carried out on samples taken from water treatment works, service reservoirs and consumers’ taps.
None of the failures of the standards in 2001 were considered harmful to consumers’ health. Each failure was assessed and, where necessary, Thames Water has taken action to prevent further failures.
Although the 2001 results are good, there are some matters, which may concern you. These are detailed below, including any steps taken by Thames Water to further improve its performance.
2. Coliform bacteria
Occasionally, coliform bacteria may be found in drinking water samples; these are not considered harmful to consumers’ health. If coliform bacteria are detected, Thames Water investigates immediately.
During 2001, low numbers of coliform bacteria were detected in the water leaving a small number of water treatment works and service reservoirs. The standard at service reservoirs permits 5% of samples to contain coliform bacteria and, in 2001, none of the Company’s service reservoirs failed the standard.
Coliform bacteria were detected in less than 1% of the water samples taken from consumers’ taps. Many of these failures could be due to the condition of the tap and not the water itself. The standard permits 5% of samples in a water supply zone to contain coliform bacteria. Only two zones failed to meet the standard and the Company has taken remedial action to prevent a recurrence of the problem.
3. Pesticides
Thames Water carried out more than 281,200 tests for individual pesticides during 2001 and all but six samples met the stringent standard. At the very low concentrations found, the pesticides detected did not represent any risk to health. This reflects the significant investment in recent years to remove pesticides from drinking water.
4. Lead
Samples do 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. These failures are usually due to the consumers’ water pipes being made of lead. Whenever a failure occurs, the householder is informed of any problems by Thames Water and advised of any action they can take to reduce lead levels in the water at their kitchen tap.
If you are concerned about the possibility of lead in your drinking water, you should contact Thames Water to see whether there is a problem. A leaflet about lead in drinking water is available from DWI free of charge and can also be found on the DWI web site.
Six of the 1,452 samples taken by Thames Water failed the standard for lead during 2001.
5. Iron and manganese
These two parameters provide a good indication of the overall condition of the mains used to distribute drinking water throughout the area of supply.
During 2001, eleven of the 2,813 samples taken for iron failed the standard. This is similar to 2000. Only one sample of the 2,308 taken for manganese failed the standard which is also similar to 2000. This reflects the impact of the programme of work being carried out by Thames Water to renovate its distribution system. Since April 2000, Thames Water has renovated 502 km of water mains. This improvement programme, which covers most of the area affected by the failures, is on-going with Thames Water being required to renovate a further 430km of mains by June 2002.
6. 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 drinking water, New regulations require water companies to sample continuously and analyse daily for Cryptosporidium in the treated water at potentially vulnerable sites.
It is a criminal offence to exceed the new treatment standard for Cryptosporidium.
During 2001, Thames Water has fulfilled its requirement to carry out continuous sampling and monitoring at 20 of its sites that were identified as being at significant risk from Cryptosporidium. The Company is required to tell DWI of any failures to meet the treatment standard. Thames Water reported no failures during 2001.
As part of the new regulations, the Company is committed to programmes of work to reduce any potential risk from Cryptosporidium at eight sites.
7. Drinking Water Quality Incidents
DWI regarded seven of the events notified during 2001 by the Company as incidents. The details are shown below.
Six of the incidents, assessed by DWI, was of short duration and the Company took remedial action. Ten recommendations were made mainly regarding sampling, communications and procedures. One of these incidents from 2001 remains under consideration.
In 2001, DWI also assessed three incidents that occurred in 2000.
Summary of water quality incidents reported in 2001
Type of incident
No.of incidents
Assessment completed
Areas affected
Supply of discoloured water
1
Yes
Bexleyheath (January)
1
No
Parts of Oxford (July)
Loss of supply
2
Yes
Chinnor (August); Part of E10 in London (December)
Microbiological contamination of supply in distribution
1
Yes
Bexleyheath DA7 (August)
Supply of water with taste and odour
2
Yes
SW18 part of London (September) Ramsbury, Wiltshire (November)
8. Further information
If you would like more information about drinking water quality the following leaflets are available free of charge from DWI and can also be found on the DWI web site:
What do we do?
How good is the drinking water?
Problems with your drinking water
Chlorine, smell and taste
Discoloured water
Lead in drinking water
Private water supplies
Water hardness
Tap water, where does it come from and how is it made safe to drink?
Using lead-free solder for drinking water fittings
DWI reports on each water company
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Drinking Water Inspectorate,
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Telephone : 020 7944 5956 - Facsimile : 020 7944 5969
E-mail: dwi.enquiries@defra.gsi.gov.uk
Published 10 July 2002
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