How Do Water Towers Work?

As infrastructure goes, water towers are pretty picturesque. Some people turn them into houses once the city no longer needs them. The designers at Pop Chart Lab once created a visual ode to New York City’s water tower taxonomy. But why exactly does water need to be stored hundreds of feet above the city?

Why Water Towers Need to Be Tall

Most water towers are pretty simple machines. Clean, treated water is pumped up into the tower, where it’s stored in a large tank that might hold a million or so gallons—enough water to run that particular city for a day. When the region needs water, water pumps utilize the pull of gravity to provide high water pressure. Because they work with gravity, they have to be taller than the buildings they’re providing water to in order to reach the highest floors. Each additional foot of height in a water tower increases water pressure by .43 pounds per square inch.

Here's a basic diagram of what a water tower system looks like:

Keeping water high off the ground plays another important role for a city infrastructure. It allows regions to use smaller water pumps.

In general, water demand for a city fluctuates throughout the day. Lots of folks are taking showers before work and school, but fewer people are running a lot of water at 3 a.m. Without a water tower, the municipality would have to buy a water pump big and powerful enough to keep up with peak demand in the mornings, which would then largely go to waste during less busy parts of the day for water usage (plus incur extra costs).

Instead, municipalities can buy a pump just large enough to satisfy the region’s average water demand for the day, and let the power of the water tower take over during the times with demand that exceeds the pump’s capabilities. When water demand goes down at night, the pump can replace the water in the tower. Also, if the power goes out and the city’s water pumps fail, the water tower can keep water running smoothly for at least 24 hours.

Take a Water Tower Tour

Go inside a water tower in Edmond, Oklahoma:

And in Bloomington, Minnesota:

And here's a 1-million-gallon water tank getting cleaned:

The Important of Water Tanks

While water towers generally seem like the product of a bygone era, they’re still very much relevant today. The Louisville Water Tower in Kentucky, built in 1860, is the oldest surviving water tower in the country, and it's still in use. In New York City, millions of people still get water from water towers, though it's one of the last large cities to rely on the system. Stored on top of tall buildings, these water towers provide the pressure for water to flow even if the electricity goes off (especially during a fire).

And, of course, one cannot discount the cultural importance of the water tower:

Every city deserves a skyscraper-sized civic monument to its favorite crop. Or beverage decanter.

A version of this story ran in 2015; it has been updated for 2023.