But in publishing its annual report covering England and Wales yesterday, the inspectorate said the overall picture was one of sustained improvement for most of the contaminants it monitors.
Shortages had forced the water companies to change the way they used their mains, tapping into new sources and pumping water in the opposite direction to its normal flow. This had stirred up sediments which had lain still for decades, turning the water rusty brown
Chief inspector Michael Rouse said there had been several instances when mains replacement work had been done carelessly, leading to discolouration and odour in the water supply.
The smell comes from algae and organic material dissolved in the water which microbes feed off, and the warm summer temperatures of recent years had helped bacteria flourish.
``It applies to almost all of the companies,'' Mr Rouse told a press conference in London. ``In some cases it has just been careless operation of the system.'' He said he was urgently requesting the water companies to improve their working methods.
But while the number of failures in water samples tested for bacteria, turbidity (discolouration) and odour had risen in the past few years, Mr Rouse said there was no threat to public health because the standard for a pass was set so high. The number of test passes for lead, pesticides and nitrates had all risen steadily over the past five years, reflecting the improvements the water companies had been making to comply with the European Union's drinking water directive. So had the number of water supply zones where the standards were met.
Overall, only 0.3 per cent of the three million tests for tapwater quality carried out in 1996 failed to meet standards, compared with 1.5 per cent in 1992.
The tests are done by the water companies themselves, with the inspectorate auditing their testing procedures. The report reveals marked differences between the companies' performances.
North Surrey fared worst, with 1 per cent of its 18,453 samples failing quality tests. The Cholderton and District Water Company, which serves just 2,500 people in two Wiltshire villages, registered a perfect performance, with not one failure among its 250 samples.
Of the big 10 water and sewerage companies, Thames, South West, Welsh and North West Water performed worst, with 0.5 per cent of their samples failing. Yorkshire, Wessex, Severn Trent and Northumbrian did best, with a failure rate of just 0.2 per cent.
Mr Rouse pointed out that between 1990 and 1993 the inspectorate launched no prosecutions for the criminal offence of supplying water unfit for human consumption. Since then, however, it had concluded four prosecutions.
Friends of the Earth water campaigner Mike Childs said the annual report was far too optimistic about lead, because it used an outdated standard of a maximum concentration of 50 micrograms per litre of water.
The World Heath Organisation now agreed on the need for a tougher standard of 10 micrograms per litre.
``The Drinking Water Inspectorate tells us 20 per cent of the population receive water with lead concentrations above that,'' Mr Rouse said.
``We need an open and honest debate with the Government and the water companies about how to tackle this issue. We know lead can damage the development of children at low concentrations.''Reuse content