Bethpage Water District Blog

Friday, December 7, 2018

How tall is the elevated tank and why do we need them to be elevated?

How tall is the elevated tank and why do we need them to be elevated?

    Elevated water tanks dot the skyline across Long Island, the country and the world. They are the source of pressure within a distribution system. Each time you turn on a faucet and water flows out, it is due to the gravitational force of the water stored at an elevated height.

    This is a great way to utilize natural forces to provide pressure without having to use electricity to “boost” or pump the water into the system. Most districts have their own elevated tank to supply to their distribution system. Some districts that have many steep hills or sharp grade changes, like on the north shore of Long Island, use pressure zones. They can automatically or manually open and close valves to maintain a safe an adequate pressure within their distribution system.

    Bethpage does not have pressure zones and predominantly runs downhill from north to south. Our water tank at Adams Avenue is 140 feet tall but the height of the water when the tank is full is 130 feet from the ground. That height creates 56 pounds of pressure per square inch (psi) at the bottom of the tank. Our district ranges from 48 psi in the northern most areas to 90 psi at the southern tip. This is all due to gravity and the fact that Bethpage runs downhill from north to south; the further south of the elevated tank, the greater the pressure. The water level within the Grumman Road elevated tank is exactly the same height as the tank at Adams Avenue.

    Both tanks “float” on the pressure of the distribution system, they HAVE to be the same height, otherwise one tank would overflow as the other tank tried to become full.

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