A stunning example of Victorian architecture was revealed to the public for the first time in half a century this week – but it will soon disappear from view once more.

Ham & High: Residents get close to Kidderpore Reservoir. Picture: Nigel SuttonResidents get close to Kidderpore Reservoir. Picture: Nigel Sutton (Image: © Nigel Sutton email pictures@nigelsuttonphotography.com)

Hampstead’s historic Kidderpore Reservoir, which was built in 1867 and is one of only a dozen brick reservoirs in the capital, has been concealed by an aluminium cover and 12 million litres of water for decades.

Ham & High: A contractor gets in among the arches at Kidderpore Reservoir. Picture: Peter DevlinA contractor gets in among the arches at Kidderpore Reservoir. Picture: Peter Devlin (Image: Peter Devlin)

However, this week its neighbours caught a rare glimpse of the structure in all its glory after the water was drained and the roof peeled off to expose row-upon-row of majestic Victorian arches.

Tracy Lawson-May, a physiotherapist whose home backs onto the reservoir, and who joined one of the close-up viewings hosted over two days, said: “It’s fantastic to see a Victorian structure that is nearly 150 years old but remains just as it would have originally been built.”

It was the first time since the 1960s that the impressive brickwork has been seen – and soon it will be under wraps again.

Having last been replaced in 1963, Thames Water has hired civil engineering contractor GBM to install a new concrete cover to boost security.

Some who attended the visits were surprised to learn that the reservoir was there at all. It is hidden behind the houses of Platt’s Lane, Ferncroft Avenue and Kidderpore Avenue, and visible only from their back windows.

West Hampstead resident Marilyn Brooks said: “I never even knew it existed and it’s a fantastic opportunity to see it.”

Steve Pape, a chef lecturer who has lived in Ferncroft Avenue for 30 years, said: “As soon as they took the roof off, I was very intrigued about the brickwork.

“It was definitely worth a look, though it’s a shame we can’t go down in the bowels to get a greater appreciation.”

While engineers have relished getting among the arches, members of the public were forbidden from clambering down in the name of safety.

Thames Water took the opportunity to scour the basin and arches for wear and tear, but the Victorians’ sturdy handiwork has ensured that they remain in excellent condition with no repairs needed.

The new roof should be in place by January 2015 and the reservoir will supply 11,000 households once it is up and running again.

Kaye Hargen, project communications adviser with GBM, said residents were invited as a “thank-you” for putting up with the works.

She said: “We want to be good neighbours and treat people as we would like to be treated.

“There has been a lot of interest and people have been stunned to discover that this has been in their back garden.”

Neil Franks, Thames Water contract manager, said: “Even as water industry engineers, we rarely get to see this kind of thing.”

He added: “It will be a shame when we have to once again conceal the arches, but we do need to protect the treated water within the reservoir and keep local homes and businesses supplied with water when they need it.”