You may not notice them, but rooftop water tanks are extremely common in the Big Apple. These all-important structures are essential to our way of life, providing water not only for daily use, but also for fire-suppressing sprinkler systems. In fact, after the turn of the 20th Century, the institution of new safety codes requiring sprinkler systems ultimately led to the development of rooftop water tanks, as it highlighted the need to fix the weak water pressure above the fifth floor in taller buildings. Water pressure is, after all, gravity fed. Without a rooftop tank, higher floors would have suffer from weak water pressure, if they were able to get water at all.
Roof tanks generally range in size from 7,500 gallons to 20,000 gallons, though as time has gone on, both the size and number of tanks being installed on NYC rooftops have increased. Some of the increase in the size of tanks is related to environmental and conservation concerns.
New York City law requires that rooftop water tanks be emptied, scrubbed down with a chlorine solution, and flushed out several times before being refilled, at least once a year. After this process, a sample of the water from tanks that are for daily use, or a combo of daily use/fire suppression must be certified as safe and potable by a qualified laboratory. The annual inspection and cleaning of a tank for a residential building costs roughly $1,000 or so per tank.
Rooftop water towers are also required to have annual inspections and file proof of an annual cleaning with the Health Department. Tank maintenance companies in the city usually handle that paperwork. Failing to file with the Health Department could cost a building owner or board a fine of $2,000.
In cold weather, the New York City Fire Department requires that the temperature of the water in roof tanks be periodically checked to prevent freezing. A frozen water tank can create a life threatening liability if the fire suppression sprinklers fail.
Some of the common signs that a rooftop water tank needs to be repaired or replaced are rather obvious, such as leaks coming from the tank, or exterior mold growth or sponginess in a wooden tank, both of which are signs of leakage. All of these signs indicate a problem, as does any rusting of pieces of the tank’s superstructure. Given the large amount of weight contained within a water tank, rust should not be ignored.
With a proactive attitude toward maintenance and inspection, your building’s roof tank should last 20 to 25 years. However, failure to heed warning signs could be catastrophic.