ELI5 : Why are water towers shaped the way they are ?

Read the Story

Show Top Comments

The sides are round because that’s the most efficient/biggest volume you can get for that amount of material. The bottom is round so you can put one drain in the middle. The top is round so that rain and eldritch horrors beyond your comprehension will roll off the top and not pool in the middle. Then you raise it up enough to get the pressure you need. Then you make it wide enough to be stable at that height. Then you make it big enough to hold all the water you need.


The concept is to pump the water up into the tower at night when electricity usage is low and rates are cheap, and then let it gravity feed back down during the day when people are awake and using water. The most basic design for this is just a big cistern up on top of some support structure. Older towers may have wooden or steel framework supports, never ones often look more like big onion bulbs on a stick. They’re rounded off because circles are stronger structural shapes than squares. Squares have a tendency to rupture in the center.


Water towers can be a few different shapes, but generally for structural strength, they are circular. Fewer weak points in a circle.


Water towers are tall to maintain consistent pressure. Water pressure depends on the “depth” of water (or height if it’s above ground). So by having a long pipe leading up to the main tank, the water pressure will be high. Then the main storage capacity is up high, so whether the storage tank is full or nearly empty, the pressure is still high. Another way to think of the water pressure is that water stored at a high point wants to “flow downhill” into the pipes of houses etc. If the tank was on the ground there would be less pressure or there would only be pressure when the tank was almost full, and very little pressure when it was empty. This means a lot of the storage capacity of the tank wouldn’t actually be useful because you could never drain that water out


The role of water towers is to provide not just storage but pressure, from the water being at a height. Since the goal is is to have as much water as possible as high up as possible, it makes sense to have small base and then a strong, high-volume shape high up. Round shapes are both very strong and have high volume for their size, so most water towers are some kind of round shape on top. If they were just a cylinder, a bunch of the water inside wouldn’t be high up, so that’s no good. So they use a big round part up high, and a slim pipe down to the ground.