Test on water supplied to Shropshire homes in the Bridgnorth area as well as Wolverhampton showed that too much fluoride was last year put into the water supply after a new dosing system at Severn Trent Water failed.

A routine sample on July 1st 2008 found treated water at the works contained 2mg of fluoride per litre of water – which is twice the target level, it said.

The Drinking Water Inspectorate said a fault happened at the pumping station which supplies 29,000 homes between Bridgnorth and Wolverhampton last June.

Severn Trent Water apologised for the error said the water had still been safe to drink.