People used the waters until the 1970s

Previous theories suggested the water lay under the Mendip Hills up to 20 miles away.

But some geologists now believe the source is a mile underground very near the historic city, where it emerges at 45C to 47C.

It is believed the water has been underground for at least 1,000 years and possibly much longer.

The research has been carried out to coincide with the development of a new spa in Bath.

Interim project manager Keith Mitchell said: "The aim is to look at the original source of these springs so we can protect them.

"There is nothing concrete proving the water is from the Mendips or elsewhere.

Further research

"We have undertaken further studies with geologists and they have come up with one or two theories."

Research is to continue and the latest theories will be published early next year.

The new spa, which is still being developed, will allow public bathing for the first time since 1978.

Centre closed

Nobody has been able to use the hot baths since the NHS closed its treatment centre in the city.

Previous attempts to restore the spas have failed because of cost and concerns over the purity of the source of the water.

Under the �19m scheme, former spa buildings are being renovated and new pools opened.

The developments are near the famous Roman baths in the city centre.