Rooftop water tower

Rooftop water towers on apartment buildings on East 57th Street in New York City. The structures seen here illustrate three architectural approaches to incorporating these tanks in the design of a building. From left to right, a fully enclosed and ornately decorated brick structure, a simple unadorned roofless brick structure hiding most of the tank but revealing the top of the tank, and a simple utilitarian structure that makes no effort to hide the tanks or otherwise incorporate them into the design of the building.

A rooftop water tower is a variant of a water tower, consisting of a water container on a roof of a tall building.

This structure supplies water pressure to floors at higher elevation than public water towers.^[1]

As building height increases, the vertical height of its plumbing also increases. This produces a large water column and the weight of this water produces very high pressure at the bottom of the column. Normally, this would require very thick (heavy schedule) plumbing to survive the pressure. Fittings at the bottom of the column would need pressure reducing valves to operate normally, and municipal water pressure would need to be very high to supply pressure to the top of the column.

Instead, the plumbing at various levels of the building are often sequestered, with pressure supplied from a rooftop water tower instead of the municipal supply. The tower itself is fed by a pump and a relatively high pressure line that carries water to the top of the building from the pipes below.

References

1. Joseph, Sean (7 April 2009). "Water towers: NYC's misunderstood icons". amNewYork. Retrieved 6 August 2016.