Official: London tap water is the best in Britain

London's tap water has been rated the best in Britain by scientists.

The Drinking Water Inspectorate's annual report into quality across the UK found water in the Thames region passed a stringent set of tests 99.98 per cent of the time.

Tests were carried out on 168,000 samples from the region, measuring 40 different aspects of water quality including taste, odour and colour.

The results beat every other region. The worst performerwas the North with a 99.94 per cent pass rate.

It is a boost for the Evening Standard's Water On Tap campaign. Evening Standard aims to get London's bars and restaurants to offer tap water to customers as a matter of course, rather than environmentally unfriendly bottled water.

Thousands of businesses have signed up to the scheme, including Antony Worrall Thompson's restaurants, Jamie Oliver's Fifteen and Aldo Zilli's Zilli Fish.

However, water firms are being warned not to rest on their laurels. Professor Jeni Colbourne, chief inspector of drinking water, said: "Although drinking water for the year was generally of good quality, overall the industry made no further progress.

"The national figure for 2007 was 99.96 per cent, the same as it

was last year and the year before."

The report highlighted problems caused by older pipes in the London area, which are slowly being replaced by Thames Water.

It said: "In the urban areas of the Thames region the most significant potential risk to public health is that of consumer exposure-to lead in drinking water. This risk remains in places where lead pipes and plumbing exist in older properties."

There was a rise in the number of enquiries Thames Water received from customers about water quality, from 27,000 calls in 2006 to 42,000 last year.

However, it is believed the higher volume was largely due to more Londoners drinking tap water - since Thames received the lowest rate of customer complaints about drinking water quality.

David Owens, chief executive of Thames Water, said: "Our drinking water is better than ever and we're rightly proud of it.

"Our research shows customers give the highest priority to the quality of their drinking water. These results, which have been made possible through funding for additional investment from customers' bills, should reassure them that this is our top priority and will continue to be so."