MPS will decide to today whether health officials should have the power to add fluoride to drinking water.

Fluoride is naturally occurring in water in Hartlepool and is already added in areas of north Durham.

However there is growing opposition among MPs, who have a free vote on the issue, because there is some evidence linking fluoride to increased risk of cancers, hip fractures, kidney problems and birth defects.

Water companies, including Northumbria Water, do not have to comply with local health authority guidelines on fluoride. But if the bill is passed, health officials would be able to order companies to add the chemical to water.

The County Durham and Tees Valley Health Authority said it hopes to carry out a public consultation as early as next year if the Water Bill becomes law. If residents are in favour, fluoride would be added to all drinking water in the area.

Dentists have cited figures revealing that children in fluoridated areas, such as the West Midlands, have far fewer rotten teeth. The average five-year-old in County Durham and Darlington has 2.06 decayed, missing or filled teeth, compared with 1.12 in Birmingham, 1.0 in Walsall, 0.93 in Coventry and 0.67 in Dudley.