Difficult year for drinking water, says DWI

The days of water companies constantly improving their compliance with drinking water quality standards appear to be over, with the Drinking Water Inspectorate’s annual figures showing no progress. The number of ‘incidents’ affecting quality has also risen for the fourth year in succession.

Water companies failed to improve compliance with drinking water quality standards in 2007, according to the Drinking Water Inspectorate’s latest annual report.1 The figure for 2007 was 99.96% in England - the same as the previous year - and 99.92% in Wales - a deterioration from 99.94% in 2006.

The figures are based on the results of 1.3 million monitoring tests for 40 different chemical and microbiological parameters.

Compliance with iron and lead standards rose in the year, the inspectorate notes, although there were drops in compliance with nitrate and trihalomethane disinfection by-product standards.

On microbiological quality there were slight improvements, but companies reported problems with service reservoirs which store treated water. Although companies blamed problems on heavy rain during the summer, the inspectorate takes the view this merely highlighted existing structural weaknesses.

These were graphically illustrated by photographs of pigeon, rabbit and rodent bones recovered during the clean-up of an unspecified service reservoir. Compliance with microbiological standards in these reservoirs fell from 99.96% in 2006 to 99.90% across England.

There was also a rise in ‘incidents’ affecting water quality. Water firms are obliged to report events that may affect the quality or perception of the quality of drinking water. These are investigated by the inspectorate and classified as incidents where actual or potential effects occur. More events were reported in 2007 and a greater proportion classified as incidents than in 2006.

The most notable incident of the year was the flooding of Mythe water treatment works in Tewkesbury which left 340,000 without tap water (ENDS Report 391, pp 32-35 ). A total of 110 incidents were reported in England and 18 in Wales. This is well up on 2006, when the figures were 84 and 14 respectively. The number of incidents has increased over the last four years (see figure).

The DWI particularly rounds on the north of England where events rose from 25 in 2006 to 46. Incidents reported by Yorkshire Water and United Utilities doubled on the previous year.

Notable incidents included a failure of a United Utilities chlorine dosing system and its back-up, the supply of discoloured water at many locations in Sheffield and Doncaster, and the supply of musty-tasting water in Hull following an algal bloom in a reservoir.

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