Underground water pocket at 60ºC could provide on-tap supply and 'green' electricity for Barcelona town

This could open the door to free, natural hot tap water, and also be converted into electricity to fuel the whole of the town, Santa Coloma de Gramenet.

The thermal water pocket was in fact discovered in 2004 when workmen were building the metro Line 9 from Barcelona city, but it is only now, after more recent studies, that experts have realised just how unique it is.

It could have the same heating and hot water potential as the underground artesian aquifers in nearby Caldes de Malavella and Caldes de Montbui.

Geologist Enric Vázquez, leading the excavation team, says the subterranean well is the only one of its kind within the Barcelona metropolitan area, and is 'unusual' because the water circulates around non-porous granite rock, meaning it is fresh water and not salty.

Most thermal aquifers contain salt water and are not suitable for human consumption, although they have great potential as renewable energy providers.

Mayoress of Santa Coloma, Núria Parlon, says both the temperature and the sheer quantity of water means the underground well could be used to set up thermal spas as well as hot tap water and electricity.

“We want to make use of it in some way or another, because its characteristics and the amount of water it contains are very significant for the town's future,” Sra Parlon says.

“We're very excited about this, and we now intend to work out what the costs would be to use this unexpected source.”

When it was found 12 years ago, experts did not consider it very important and, although studies have been commissioned since, they were never treated as a priority.

Only now that geologists confirm the huge value of this natural source has Santa Coloma begun to think about how it could be an exceptionally useful resource for the town.

Other countries worldwide have found underground hot springs to be a godsend and have taken full advantage of them.

Iceland, for example, uses only renewable energy and zero fossil fuel, thanks to the numerous underground heated wells beneath the island nation's surface.

All electricity comes from the thermal aquifers, as does tap water.

It is perfectly safe to drink from the cold tap in Iceland, but tourists are always warned water from the hot tap is extremely heated, and assured that the sulphuric smell that comes with it is no cause for concern.

On the other side of the planet, in the north-western New South Wales outback close to the Queensland border in Australia, the town of Lightning Ridge sits on Artesian bore wells which have enabled giant hot tubs to be created (pictured), and are a popular recreational area residents and visitors can enjoy free of charge.

Thanks to the Artesian bores, pure mineral water comes out of the taps and can be drunk safely.