How water towers work
By Marshall Brain
http://www.JewishWorldReview.com | (MCT) Your neighborhood water tower is one of those things that blend into the background. You see water towers everywhere, especially if you live in a flat area full of small towns, but you may never give them a second thought. It turns out that the water tower is an important part of the water system in your community.
How important is the water tower? Think about this: when was the last time you had a "water failure?" We have power failures on a pretty regular basis, but how often does the water go out? Not very often. The water tower is the thing gives the water supply this kind of super reliability.
A water tower is a big, elevated tank filled with water. A typical water tower is about 165 feet (50 meters) tall and the tank may hold a million gallons of water or more. There is a big pipe called a riser that connects from the water main in the ground up to the tank.
Here's what happens. Somewhere in town there are massive pumps that send pressurized water into the water mains for your community. These mains are big pipes carrying thousands of gallons of water every hour. If the pumps can move more water than people in the community are using at that moment (late at night say), the extra water goes up the riser into the water tower tank. If people are using more water than the pumps can produce (for example, when everyone takes a shower in the morning), water flows down from the tank back into the mains. If the water tower fills to the top, the pumps can turn off to save energy.
Water towers are tall to provide pressure. Because of gravity and the weight of water, each foot of height provides 0.43 PSI (pounds per square inch) of pressure. So a 165-foot-tall water tower provides 71 pounds per square inch of water pressure. The water tower must be tall enough to supply between 50 and 100 PSI of pressure to all of the houses and businesses in the area of the tower. So water towers are typically located on high ground, and they are tall enough to provide the necessary pressure. In hilly regions, a tower can sometimes be replaced by a simple tank located on the highest hill in the area.
A water tower's tank can be quite large. An in-ground swimming pool in someone's backyard might hold 20,000 or 30,000 gallons, and a typical water tower might hold 50 times that amount. A water tower's tank is sized to hold about a day's worth of water for the community served by the tower. If the pumps shut down (for example, during a power failure or because of a repair), the water tower holds enough water to keep things flowing for about a day.
In a city, tall buildings often need to solve their own water pressure problems. Because the buildings are so tall, they often exceed the height that the city's water pressure can handle. So a tall building will have its own pumps and its own tanks. In a city like New York, you will see water tanks on top of tall buildings.
Another interesting fact about water towers - they can affect your insurance rates. During a fire, the water demand increases significantly and may greatly exceed the capacity of the pumps at the water plant. A water tower guarantees that there will be enough pressure to keep water flowing through the fire hydrants. Fire insurance rates are normally lower in a community in which the water system has water towers.
What about freezing - why don't water towers freeze solid in the winter? One reason is because so much water flows in and out every day, and the water coming from the mains in the ground is relatively warm. In really cold areas, heat tape and insulation on the riser keeps water in the pipe from freezing. And in excruciatingly cold places, there may even be a heater system that keeps the water in the tank from freezing.
The next time you are out driving around, especially if you are driving through a series of small towns, take the time to notice the water towers. Now that you know how they work, you will be amazed by how many you see and by all the different forms they take.
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