New York Stories

David Usborne braves the trolls said to live in the city's rooftop water tanks and is cheered by the sight of the newest 'tree' in Central Park

We are scaling the second of a series of steel ladders on top of a 16-floor apartment building in midtown Manhattan when my guide, John DeGeorge, recalls a colleague missing his footing last year. "Yeah, he fell 20 feet. Smashed up both his ankles pretty bad. He don't do this work no more."

The work is building and maintaining those round wooden water tanks that you see perched on the roofs of scores of buildings in New York. For eight years, John has been on one of the crews from Rosenwach Wood Tanks, the only company left in the city still building and installing new tanks.

This morning, John, accompanied by Manuel, his brother-in-law, is on a cleaning job. The tank on this roof is 14 years old – they generally get replaced every 30-odd years – and hasn't been scrubbed for two years. Once it has been emptied down a drain pipe on to the street – the last few inches are thick with pond-like gunk – it is Manuel who climbs all the way inside with a bucket, yellow rubber boots and a mop.

From up here, you can scan the horizon and see scores of the tanks, like wine barrels on stumps. According to some, they are the homes of mythical rooftop trolls that only come out after midnight. Far from being relics of a bygone time, as I used to imagine, they are working parts of every building they grace.

Manhattan doesn't have the water pressure to get supplies any higher than the sixth floor. Some modern buildings have internal pressure systems driven by pumps. The older ones have single pumps that drive the water up to one of these towers. Gravity then takes it down again.

This tank, measuring 15ft across, made of yellow cedar and held together by steel bands, feeds the sprinkler system and fire hydrants, not people's kitchens and showers. I am relieved to hear this, given the colour of the water.

John, 28, never tires of working with the tanks. "Some people think they are eyesores. But I love 'em. They are what sets this city apart from other places." It takes him and a small crew just a day to take down an old tank and build a new one in its place.

This is a precarious place of work, however, and it is not for everyone. "Guys who are afraid of heights, you usually find out pretty soon. They are gone the next day."

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If there is such a thing as trees from outer space, one has surely landed in Central Park. It is made of shiny steel, and rises 50 feet from the ground with a thick trunk and all the requisite branches and twigs quivering in the winter wind. If you come across it unawares, you will be thrilled, certainly, and perplexed.

The tree is, of course, a sculpture, placed in the park until 30 June as part of this year's Whitney Biennial project. Conceived by Roxy Paine and called "Bluff", it is made of 5,000lbs of cantilevered branches. As people approached it on a recent afternoon, every one of them broke into a smile. Until now purists in the city have successfully blocked attempts to use Central Park as a stage for artworks. That taboo, however, seems to be over. If other pieces proposed for the park are as dazzling as "Bluff", few people will mind.