The Physics of Water Towers

By Andrew Logemann

Posted March 17, 2025

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Transcript

D: On my way into work this morning I must have passed five different water towers. Do those towers serve an important purpose these days?

Y: Well, Don, when is the last time you turned on a faucet in your house and didn't get any water?

D: Hmmm! Now that you mention it, that's never happened.

Y: Then you can thank your local water tower! Water towers take advantage of the force of gravity to provide pressure for the water they contain. Every vertical foot adds point-four-three pounds per square inch to the water pressure. Towns usually keep their water pressure between fifty and one-hundred pounds per square inch, so a simple equation tells them how high to build the tower. And since a typical tower contains a full day's worth of water, the force of gravity can maintain the hydrostatic pressure of the water system even when the power goes out.

D: OK, I get it. Water towers store up water in case of emergency. Is that all they do?

Y: Actually, they serve an important day-to-day purpose as well. A city's water usage varies throughout the day, usually peaking in the early morning when many people are showering and washing. Water usage during this time can be four or five times higher than during other parts of the day. To maintain water pressure during peak hours of the day, a city could invest in a very powerful pump, but this would be expensive and wasteful, since its capacity would go unused for most of the day.

D: Let me guess: instead, the city draws on the water tower's supply of water during these hours of high demand.

Y: That's right! The water tower and the pumps work together to keep the water pressure stable throughout the day.

(Image by Adobe Stock)

Water towers are everywhere, and while they might not seem to be doing much, when was the last time you turned on a faucet in your house and didn't get any water?

For that, you can thank your local water tower! Water towers take advantage of the force of gravity to provide pressure for the water they contain. Every vertical foot adds point-four-three pounds per square inch to the water pressure. Towns usually keep their water pressure between fifty and one-hundred pounds per square inch, so a simple equation tells them how high to build the tower. And since a typical tower contains a full day's worth of water, the force of gravity can maintain the hydrostatic pressure of the water system even when the power goes out.

Water towers serve an important day-to-day purpose as well. A city's water usage varies throughout the day, usually peaking in the early morning when many people are showering and washing. Water usage during this time can be four or five times higher than during other parts of the day. To maintain water pressure during peak hours of the day, a city could invest in a very powerful pump, but this would be expensive and wasteful, since its capacity would go unused for most of the day.

So instead, the city draws on the water tower's supply of water during these hours of high demand. The water tower and the pumps work together to keep the water pressure stable throughout the day.

Learn more

Sources

Becher, Bernd and Hilla Becher. Water Towers. Boston: The MIT Press, 1988.

Messerli, B., D. Viviroli, and R. Weingartner. "Mountains of the World: Vulnerable Water Towers for the 21st Century." Ambio. 13 (2004): 29‑34.

Shepardson, Daniel P., Jon Harbor, and Bryan Wee. "Water Towers, Pump Houses, and Mountain Streams: Students' Ideas about Watersheds." Journal of Geoscience Education. 53.4 (2005): 381‑86.