An investigation is being launched into the cost of adding fluoride to the Bath area’s water supply.

Health chiefs in the city have agreed with their counterparts across the former Avon that Bristol Water should be asked to carry out a feasibility study into the potentially controversial move.

The firm supplies about half of Bath and north east Somerset and it is possible that Wessex Water, which serves the city and the rest of the district, will also be approached.

Last year, Health Secretary Alan Johnson backed the idea of adding fluoride to the water supply in areas where tooth decay is high to improve the dental health of poorer children.

He said the measure was needed to cut health inequalities between children in affluent families whose tooth brushing is supervised and those in households where they may not even own a toothbrush.

NHS B&NES – previously known as the local primary care trust – has already started the ball rolling in conjunction with health chiefs in Bristol, north Somerset and south Gloucestershire.

The capital costs of adding fluoride would be met by the Department of Health and the strategic health authority for the region, but running costs would fall to local trusts.

Bristol Water has been approached first because it serves the biggest population in the former Avon – including Keynsham, Peasedown St John and Midsomer Norton.

Initial estimates suggest that adding fluoride at Bristol Water’s three treatment plants would cost around £2 million.

The situation will be discussed by B&NES councillors at a meeting on Tuesday.

A report to the council’s healthier communities overview and scrutiny committee says that fluoridation could reduce tooth decay by around 30 per cent in children, and increase the proportion of the population without decayed teeth by 20 per cent.

Politicians will consider a 30-page report from Professor Martin Downer of the University of Manchester, looking at the logistics and implications of adding fluoride to water in B&NES.

His report says there are nine areas of B&NES with “exceptionally high” levels of tooth decay among five and six-year-olds.

These include Peasedown, Odd Down, Twerton, Southdown, Keynsham and the city centre.

He argues that fluoridation is safe and does not – as opponents claim – breach basic human rights.

Prof Downer says, however, that the cost of adding the mineral to the areas of B&NES covered by Wessex Water would be between £6 million and £8 million.

A separate report to councillors in the name of B&NES director of public health Dr Kieran Morgan suggests that this might be a sticking point.

“Flouridation may be considered desirable for the city of Bath and surrounding areas but capital costs are high and it seems that neighbouring Wiltshire, part of which would also have to be fluoridated, has no plans to pursue this course.”

There are four Wessex Water treatment works which serve Bath, but some also send water to Wiltshire too.

Last year Mr Johnson said: “Fluoridation is an effective and relatively easy way to help address health inequalities – giving children from poorer backgrounds a dental health boost that can last a lifetime, reducing tooth decay and thereby cutting down on the amount of dental work they need in the future.

“We have a duty to help the areas with the worst records on tooth decay to discuss this issue and take the necessary steps to improve their dental health.”

However, any blanket fluoridation programme would be opposed by campaigners who say the entire population will be forced to take “medication” because a minority fail to brush their teeth.

In the Irish Republic and the USA more than 70 per cent of water is fluoridated, compared to a figure of 10 per cent in Britain.