A water company has been ordered to clean up a reservoir after bacteria levels were found to be too high, writes Rebecca Smith.

Thames Water has drained part of Culham reservoir, at Culham, near Abingdon, after three tests by the Drinking Water Inspectorate last year found bacteria called coli- forms.

Both the Drinking Water Inspectorate and Thames Water insist the water, supplied to about 5,000 homes in the Culham area, was at no point unsafe to drink.

Thames Water spokesman Nick Tennant said: "The bacteria is naturally occurring. We narrowly failed the very strict tests on drinking water quality and action is being taken. We regret the coli- forms were there as they should not have been." He said various technical measures were being taken to improve water flow through the reservoir to prevent the problem recurring.

Work should be finished by December. Customers should not notice any difference in supply while work is carried out as water will be re-routed from other parts of the reservoir.

A Government spokesman said: "The bacteria don't represent any threat to health and are not noticeable. They serve as an early warning and indicate that in the future there may be a route in for other bacteria and they are tested for this reason.

"This is certainly not exceptional and lots of companies have this.

Their presence may indicate a seepage from rainwater or that the reservoir needs a clean."