Big cities and small towns may seem very different, but one thing they have in common is that they both have water towers. You've probably seen them. They are huge tanks that rise high above the land. In big cities they are perched on top of the tall buildings, and they serve a couple of important purposes.
The first has to do with water pressure. If water is stored very high off the ground, when it is released, it has a lot of pressure as it rushes down through pipes to let us take showers and clean our dishes. If it weren't so high up, there would not be as much pressure. Our showers would be weak, and our dishes might not get clean. This is a very important reason why water towers are placed on the tops of tall buildings. The pressure from a city's water system isn't usually enough for the needs of the people inside the buildings, so the buildings get their own special pumps! The pumps bring water to the towers up on the roofs, and then when water comes from the towers, rushing downward, it has a lot of pressure.
Water towers also act as back up water supplies. If something ever happens to the main water system, the towers will usually have enough water stored so that people can continue using water normally, until the problem with the main source is fixed.
Water Pressure in Action
There's a pretty simple experiment you can do to see the differences in water pressure at different heights.
You'll just need an empty plastic soda bottle or milk jug and a pin. Have a grown-up help you poke a hole in the side of the plastic bottle a few inches from the bottom. Cover the hole with your finger, and fill the bottle with water all the way to the top.
Stay next to the sink now, and make sure the hole in the bottle is pointed toward the sink. Uncover the hole and watch the water squirt out! How far does the water squirt? Does the distance it squirts change as the amount of water in the bottle changes?
Do you think there is more water pressure when the bottle is full or almost empty? How do you think it helps water towers to have a lot of water in a very tall space?