Curiosity got the better of John Clark who had often wondered about the hole at the bottom of his garden.

He knew it was there. John had seen ancient photographs showing evidence of its existence when his garden, at Colton House in Burnsall, was redesigned.

So when he got an equally curious ally in his friend, Alan Stockdale, together they decided to explore what was there.

"My wife, Pam, wasn't too happy. She was worried about what we would find down there," said John, former head teacher at Malsis School in Glusburn.

The task first involved digging out the earth and then removing a large stone flag which gave access to a brick lined shaft.

Next came the aluminium ladder and, armed with a "caving" lamp, Alan gingerly climbed down, followed by John.

What they saw was staggering. From the domed roof of what looked like a sandstone lined subterranean building, were thousands of pencil thin stalactites. The ceiling was literally crowned with them.

" It was very exciting even though we knew there would be stalactites," said John. "And to think we were possibly only the second lot of people to see it since it was built ."

The building was last explored back in the1980s when the then owner of the house ventured underground.

The entrance had been unearthed by Burnsall villager Wilf Hargraves, who had stumbled on the stone "lid" when building an ornamental garden. It was then re-sealed.

"We set about exploring the place and measured it as 34ft long, eight feet wide and ten feet high to the top of the domed ceiling," said John.

"We could see it had been a water tank. It was lined with sandstone and there were two feeder pipes that came into it. The floor was just a muddy mess but the ceiling was spectacular."

John believes the water tank was built at the time of the house construction, in 1723, or shortly afterwards and supplied the household with fresh water. At the time Colton House was one building and owned by a yoeman farmer.

The discovery also confirmed another domestic anomaly. In the corner of Pam and John's kitchen is a five foot high pump with a large brass faucet.

"We believe this was connected to the tank and fed the house. It's a fascinating thing," said John.

The installation of the tank all those years ago is part of the history of how Burnsall villagers were supplied with drinking water over the years.

The subject is explored in Eric Lodge's superbly researched book "A Wharfedale Village", a detailed study of the history of Burnsall and Thorpe-sub-Montem, published in 1994.

He has a chapter devoted to water which explores how the community eventually became linked to the mains supply following the extensive construction of reservoirs by Bradford Corporation Water Works.

Mid 19th century the supply of domestic water in the rapidly developing wool textile town of Bradford reached a critical stage. But Bradford's problem was, in some ways, to Burnsall's benefit.

Eric Lodge tells us Barden Moor seemed an ideal location to construct new reservoirs and the corporation set about building two - at Lower Barden and Upper Barden. Low Barden became operational in 1860 and High Barden was authorised in 1875.

The shanty town to accommodate the workers was at Eastby Brow, now a popular spot to enjoy the spectacular countryside. High Barden was finished and filled by Christmas 1882.

More important to the villagers was the laying of a conduit from Sandbeds beck to augment the catchment at Low Dock. Its aim was to take water from feeder streams.

It meant that two mills on Joy Beck would be deprived of a constant flow to drive the wheels. They were bought from the Tempest family and closed in 1864.

So by way of compensation to the freeholders, Bradford Water Works agreed to pipe water to three points in the village.

The result was a supply set up in the corner of the wall of Colton House, at Holly House corner and a tap on the village green.

"When the three taps were were provided one can image how much these facilities would be appreciated, especially in wintertime," writes Eric Lodge.

Demand for piped water increased and the construction of a storage tank high up the fell side enabled all homes to be connected , a second tank enabling even more water to support the installation of lavatories.