Though most water companies were hit by the dry summer in 1995 and freezing temperatures last winter, some copedbetter than others.
Mr Byatt said: "I am glad to see a number of companies continue to improve their services. However, not all companies have done so and the effect is a slower improvement than in past years."
There was only a slight improvement in the proportion of billing queries answered within five working days, while the overall performance in responding to written complaints was unchanged, though 94 per cent were answered inside 10 working days.
The number of written complaints went up by 10 per cent to 171,000, while service interruptions lasting more than 12 hours more than doubled to 130,206. There was a similar increase in households suffering supply breaks for more than 24 hours. However, the quality of drinking water continued to improve, with 99.5 per cent of tests meeting Ofwat targets.
There were also worrying variations in service standards, with some companies reporting performance levels significantly below the industry average.
Mr Byatt said he was discussing with the companies involved ways of improving matters.