More Pesticides in Less Water? 
Drinking Water Inspectorate Annual Report

The third annual report of the Drinking Water Inspectorate (DWI)(1) reviewing the quality of drinking water throughout England and Wales during 1992, has been published. The Chief Inspector, Mike Healey, expressed his satisfaction with the overall quality of public water supplies and with the role of the DWI in auditing the water companies.

Nearly 3.75 million tests for various parameters were carried out by the 38 water companies in 1992. The results of these extensive analyses, which were audited by the DWI, showed a 98.7% compliance with the relevant water quality standards.

    The number of individual pesticide determinations in 1992 was 1,007,352; an increase of 21.5% over determinations in 1991 and 86.5% over 1990. Of these 30,618 exceeded the Prescribed Concentration or Value (PCV) of 0.1 µg/l; an increase of 32.2% over 1991 and 171.7% over 1990. The number of determinations where the total pesticides exceeded the PCV of 0.5 µg/l also increased significantly to 5,061 in 1992 from 4,426 in 1991 and 1,940 in 1990.

    The massive increase in pesticide detections in 1992 is justified in paragraph 5.5 of the report which states that: “The increase is not considered to be indicative of a worsening in water quality, but rather the product of a more focused monitoring strategy”. The report goes on to say that the number of zones where pesticide PCVs were exceeded actually went down slightly in 1992. According to the DWI(2), the “more focused monitoring strategy” is a reflection of the increased sampling frequency which is required when the PCV is exceeded. Normal monitoring for pesticides takes place 4 times per year, but if the PCV is exceeded, the frequency increases to 12 or 24 times per year according to the size of the water supply zone.

    The data provided in the report does not allow for detailed analysis of the situation regarding pesticides in water, but then the report is an overview, and provides a great deal of information on overall water quality and the individual water companies. The impression regarding pesticides however, is that they are being detected more frequently and are exceeding the PCV in a higher proportion of cases. This impression is denied in the report, but is not addressed in detail.

    Discussion of the particular findings suggest that where the PCV has been exceeded, other guideline values for the same pesticides such as those of the World Health Organization (WHO), the UK Department of the Environment (DoE), or the US Environmental Protection Agency (EPA), have not been breached. The report also emphasises that even where the PCV or various guideline values have been breached, the level of contamination and the resulting exposure was far below levels known to be harmful.

    More emphasis is placed by the report on the small reduction in the number of supply zones where the PCV was exceeded. This is probably a reflection of the completion of some of the improvement programmes in water companies where breaches of pesticide PCVs had been found in the past. However, despite the optimistic tone of the DWI report, nearly 30% of supply zones did not comply with drinking water standards with regard to no pesticide content during 1992. Or, in the words of a Friends of the Earth press release: "at least 14.5 million customers in England and Wales were supplied with substandard drinking water in 1992, seven years after the legal deadline for compliance"(3). (MD)

1. Drinking Water 1992, a report by the Chief Inspector, Drinking Water Inspectorate, Department of the Environment, Welsh Office, HMSO July 1993, £25.

2. Pers. comm. DWI, 31 August 1993.

3. Friends of the Earth, "Millions supplied with polluted drinking water - 'Customers champion' tries to sell them short," Press Release 13 July 1993.

[This article first appeared in Pesticides News No.21,September 1993, page 18]