The Quality of Water is Sustained

The fourth annual report of the Drinking Water Inspectorate (DWI)  shows a continued improvement in the overall quality of drink­ing water in England and Wales. A total value of 98.91of the 3.5 million tests for all parameters complied with national and EC standards as opposed to 98.7% com­pliance in the previous two years.

The actual number of tests carried out was lower in 1993 than in the previous year by nearly 250,000. This is a reflection of the statutory requirements for sampling which allow the number of samples tested to be reduced where consistent compliance with standards has been demonstrated.
    Improvements in compliance are registered for every parameter tested except for polycyclic aromatic hydrocar­bons (PAH) which come from the lining materials of older water pipes.

Smallest improvement in pesticides
The picture for pesticides in water shows some improvement. An improvement of 1.4% was noted over the previous year for compliance of total pesticides detected, and for individual pesticides the improvement in com­pliance was 1.9%.  However, the optimistic tone of the DWI report hides some potentially worrying facts:

• In 1993 more supply zones failed to comply with the standards for individual pesticides in drinking water than for any other parameter. 27.9% of supply zones failed to comply with the standard of 0.1 µg/l for individual pesticides and 11.9% of zones failed to comply with the 0.5 µg/l standard for total pesticides;

• A higher percentage of the determinations of total pesticides contravened the legal limits than did any other parameter; 7.2% of the 56,351 determinations of total pesticides were found to be above the 0.5 µg/l maximum per­mitted level;

• The improvement in compliance over previ­ous years is smaller for pesticides than for any other parameter. 9% fewer supply zones did not comply with stan­dards for individual pesticides in 1993 than in 1991, and the reduc­tion for total pesticides was 18%. The improvements for other para­meters such as coliforms was 79%, for nitrate was 45% and for aluminium was 38%.

Several pesticides were found to exceed the legal Prescribed Concen­tra­tion Value (PCV) of 0.1 µg/l. The table shows the number of samples in which the pesti­cide was sought (determinations), and the total number of cases where each pesticide was found to con­travene the PCV.
    Atrazine and simazine, the triazine herbicides banned from non-agricultural use in 1992 still feature highly as contaminants of drinking water. Remai­ning stocks of these herbicides should have been used up by the end of August 1993, and one would hope to see them virtually disappearing from water by the time the next DWI report is published. Diuron which to a large extent has replaced the triazines, also features prominently as a contaminant.

Surprise findings
One or two unexpected pesticides are reported to have exceeded the PCV. Dwr Cymru (Welsh Water) reports contraventions for glyphosate. Glyphosate has not been found to exceed the PCV by any other water company. Indeed it is apparently technically extre­mely difficult to isolate glyphosate in water where other trace contaminants are present. It is also surprising that the product hailed so widely by industry as the environment friendly herbicide should appear in drinking water. Dwr Cymru put the contravention down to spurious laboratory results, and the authorities have apparently accepted this explanation(1).
    North East Water reported a single contravention in 1993 for dieldrin which was banned in 1989. This was reported to the NRA and resampling failed to show a presence of dieldrin. The matter was not investigated further(2).
    Mid Kent Water has on a num­ber of occasions found the banned herbicide 2,4,5-T in water from one supply, and on a single occasion in June 1993 it was found to contravene the PCV(3). The incident was reported to the regional National Rivers Authority, but no detailed investigation was carried out and no specific action has been taken. According to the NRA, the supply has in the past been contaminated by pesticides from a nearby chemical plant, but 2,4,5-T is not made or formulated in this plant(4).
    Non compliance with stan­dards does not necessarily imply con­sistent failure to meet the standards. Where a single test shows levels above the required standard, the supply zone is registered as having failed to com­ply. However, this rationalisation applies to all parameters and the high rate of fail­ure for zones to meet the required stan­dards for pesticides remains worrying.

Action considered in 35 zones
The DWI report explains that non-compliance with standards for pesticide levels in water does not imply a health hazard, but goes on to say that the standards are nevertheless legal requirements, and the DWI is charged with ensuring that they are met. It is for this reason that enforcement action is under consideration in 35 zones where levels for individual pesticides have been exceeded, and the DWI is not fully convinced that sufficient action is being taken by the relevant water companies to put things right. This is a very sig­nificant increase over the previous year when the number of supply zones for which enforcement action was con­sidered over individual pesticides was only seven.
    Many enforcement actions were withdrawn by the DWI where it was demonstrated that the water com­pany was taking adequate steps to alleviate the problem identified. This often entails the installation of equip­ment, and last year the DWI was charged with examining the technical justification for water companies spen­ding on improvement programmes.

Are pesticide levels rising?
An interesting and worrying point is demonstrated by this element of the DWI’s work. Approval for spen­ding on programmes to improve the situation regarding pesticides in water is only given where the water company can demonstrate that pesticide levels were rising and would exceed stan­dards in the future if the improvements were not made.
    Water companies are spending hundreds of millions of pounds on tech­nology to remove pesticides from drink­ing water, and the cost of moni­toring for pesticides and maintaining the equip­ment to remove them also runs into millions. This cost is passed on to con­sumers. The amount of public money spent directly or indirectly on preventing pesticides from entering water is incom­parably small.
    The latest DWI report demon­strates clearly that not only are pesticides still present in drinking water, and not only is water quality improving more slowly with regard to pesticide content than other contaminants, but also that this situation is likely to continue into the foreseeable future. The water industry and the DWI are sufficiently con­vinced that pesticide levels in water will continue to rise to authorise the expenditure on new technology to remove them. The cost of their removal will continue to fall on con­sumers and not on the polluters. (MD)

1. Pers. comm. Dwr Cymru,  26/8/94.
2. Pers. comm. N.E. Water 31/8/94.
3. Pers. comm Mid Kent Water, 30/8/94.
4. Pers. comm. NRA, 30/8/94.

Drinking Water 1993. A report by the Chief Inspector, Drinking Water Inspectorate, HMSO, July 1994, £28.00.

[This article first appeared in Pesticides News No. 25, September 1994, page 18]