Writing to English and Welsh ministers, the Inspectorate has once again confirmed high compliance with the European Drinking Water Directive. The Chief Inspector of Drinking Water said that the results are "comparable with the best presently reported in Europe". Over 99.96% of 4.25 million samples taken by water companies met standards required by European and UK legislation.

Most of the very few failures to meet standards were attributable to iron concentrations or aesthetic factors such as appearance, taste or odour rather than health issues. Companies are continuing to address iron levels and water discolouration by replacing or re-lining cast iron water mains.

 Private water supplies still a problem

The Inspector said that all European countries, including those in the UK, had identified and agreed that ‘small water supplies’ are the most problematic, not just in terms of safety and security, but also in terms of competent management, reporting and regulation. The Report said that such consensus made it inevitable that action to improve the safety of small water supplies in Europe would feature highly in the upcoming revision of the Drinking Water Directive.

In total there are 30,021 private supplies in England and Wales of which 2,540 supply more than 10m3 per day. According to the Report, the risk posed by private water supplies is again illustrated this year by two incidents where a private water supply contaminated the public water supply through an illegal cross connection.

Thames comes out on top

At water company level, six of the ‘combined water and sewerage’ companies achieved a better compliance record - the top performer was Thames Water with a figure of 99.99%. The best tap water quality can be found in the Thames region (99.98%).

However, the figures for Wessex Water were down on those reported in 2007, along with Northumbrian Water and United Utilities -  the latter two companies were below the industry average. The figure for Dŵr Cymru Welsh Water in Wales was unchanged but also lies below the industry average.

Among the ‘water only’ companies and licensees, six small companies achieved 100% compliance, while eight others reported a lower compliance figure in 2008 compared to 2007. Below the industry figure were Portsmouth Water, South East Water, Bournemouth and West Hampshire Water and Sutton and East Surrey Water, (99.89% – 99.95%). In Wales, Dee Valley Water also turned in a below average result.

Water supply management

The Inspectorate said that results at water treatment works in 2008 were mixed. Process control improved to 99.98% with figures for only four companies trending downwards. The lowest figures recorded were those of Southern Water (99.94%) and United Utilities (99.92%).

However, the general improvement in process performance had been offset by the disinfection index figures. The year as a whole was described as “characterised by deficiencies in disinfection.”  The DWI said that as a consequence, the overall industry figure had declined from 99.94% in 2007 to 99.93% in 2008 and that a worrying downward trend in the individual figures for 13 companies lay behind the figure.

Companies with below industry average figures were Bournemouth and West Hampshire Water, Dee Valley Water, Dŵr Cymru Welsh Water, South East Water, United Utilites and Yorkshire Water. During 2008, across all of the industry’s 1,286 treatment works, there were seven occasions when E.coli was detected, 78 samples contained coliform bacteria and on 120 occasions turbidity exceeded the specification. At the end of 2007, the Inspectorate was provided with new powers to deal with any persistent or serious disinfection. The Inspector commented that it was regrettable that a number of cases were already under consideration.

Service reservoirs water quality improvement

The Report described the overall industry improvement in the quality of treated water stored in service reservoirs and water towers as ”a pleasing highlight”  with the integrity index up to 99.96% from a low of 99.93% in 2007. Northumbrian Water was the only company to stand out as countering the upward trend with a year-on-year deteriorating record from 99.94% in 2006 to 99.92% in 2008.

During 2008 across all of the industry’s 4,659 service reservoirs there were 23 occasions when E.coli was detected and 168 samples contcoliform bacteria. With only a few exceptions, DWI inspectors’ assessments of these failures verified that companies were acting more effectively to rectify the causes which comprise a mixture of structural defects and poorly designed or maintained sampling facilities.

Lessons still to be learned from water quality incidents

Despite the generally favourable conclusions about the good quality of drinking water, the Inspectorate drew a note of caution and said it had not been a good year in terms of the impact of water supply management on consumers. Inspectors this year classified 144 notified events as a water quality incident impacting on consumers, which compared unfavourably with the totals of 129 reported in 2007 and 98 in 2006.

The Chief Inspector said that while on its own, the absolute number of incidents per year was not a meaningful indicator, the three year consecutive rise in the number of incidents merited closer scrutiny.