London's Australia House is a building with an aura of old magic and intrigue. In medieval times, the site was considered sacred, frequented by monks. In recent years, the building's arcane marble architecture has been used as a movie set for "Harry Potter" films (think Gringotts Bank).

Perhaps it's only fitting that a scientific investigation recently uncovered a hidden well in the building's basement that dates back 900 years, to Celtic times, that is still full of spring water. And incredibly, the immaculate water remains fit to drink, reports Australian Broadcasting Corporation.

The well is thought to be one of around 20 throughout London that have been covered by roads and structures over the centuries and forgotten. Not all of the locations of these springs are known, and even fewer are accessible, making this Australia House well particularly unique.

The spring itself is fed by the Fleet River, which today is a subterranean creek covered by the streets of London. The only reminder that this waterway still persists is London's Fleet Street, which was named after it.

According to Alexander Downer, Australia high commissioner to Britain, writings from a medieval monk were found that referenced water from this spring as “sweet, wholesome and clear.” The well was likely of holy significance at one time.

Over the years the spring water may not have been quite so pure as it is now and was then. For instance, in Roman and Anglo Saxon times, the Fleet was a major river that was gradually transformed into a noxious, polluted ditch as the city grew around it.

Today, however, the waters have been officially declared safe. The water was tested by the Latis Scientific laboratory for a score of hazardous microbes including E. coli, Enterococci and Clostridium perfringens, but came back with a clean bill of health.

"Better than tap water," declared Australian public servant Duncan Howitt.

Bryan Nelson ( @@brynelson ) writes about everything from environmental problems here on Earth to big questions in space.

900-year-old 'holy well' discovered that still has clean, drinkable water
The well was uncovered in the basement of an old London building that was also used as a 'Harry Potter' set.