To watch the tankmen practice their craft is to witness a construction technique that has transcended time, as was evident one day not long ago when a Rosenwach crew was building a water tank on the roof of a 24-story hotel rising near the Empire State Building. Three men moved nimbly around a narrow, rail-free scaffolding almost 300 feet above the street, while two others handed up planks from the rooftop below. It took less than two hours to construct the body of the tank, setting vertical boards in place using only a hammer and a rope.

Modern tankmen build in materials other than wood, but they don’t rave about it. Steel tanks cost up to four times as much and must be properly maintained to avoid rusting. Wood insulates better than many other materials, keeping water cool in summer and preventing freezing in winter. And wooden tanks are visually interesting.

“They’re an icon; they’re part of the tradition of this city,” said David Bonilla, a project manager for Rosenwach. “There’s just nothing that works as well.”

Atop the hotel roof where the tankmen were working this day, 150 wooden water tanks could easily be seen, distinctive silhouettes that resemble grain silos on stilts. Although they come in all shapes, sizes, and states of repair, most still play an active role in managing the city’s water supply. Indeed, new tanks are being built every day, in part because of the current building boom.

Their roots go deep into the city’s history. According to Kathleen Hulser, a historian with the New-York Historical Society, indoor plumbing began replacing well-drawn water in the 1840s. During those years, natural water pressure could supply all of the city’s buildings. Tanks began sprouting up in the city about 50 years later, at the same time as the tall buildings themselves, a symptom of the growth that followed the Civil War. Rooftop tanks were used because local water pressure was too weak to raise water to the upper stories; instead, buildings over six stories use a pump to fill tanks, after which gravity goes to work. This remains the case.