Toilets

Last updated: July 8, 2008.

Toilet, lavatory, loo, WC, John, crapper, can—it's amazing we have so many names for something we care to talk about so little. Toilets are hardly the most glamorous of inventions, but imagine trying to live without them. About 40 percent of the world (some 2.6 billion people) are in that unhappy position, lacking even basic sanitation. At the opposite end of the scale, in Japan, people have amazing electronic toilets that do everything from opening and closing the lid automatically to playing music while you use them. Most of the world's toilets are more modest than this, but they're still pretty ingenious "machines." Let's take a closer look!

Photo: Like most new toilets, this low-flush model is designed to save water. The two buttons on top let you choose whether to flush with a large or a small amount of water.

Flush and go

At first sight, toilets seem quite simple: you have a waste pipe going through the floor and a tank of water up above (called a cistern) waiting to flush into it when someone pushes a button or pulls a lever or a chain. Most flush toilets are purely mechanical: pull the chain and the cistern empties through the force of gravity, washing the bowl clean for use again. They are literally mechanical because they flush and refill using levers inside—and levers are examples of what scientists call simple machines.

There's a little bit more to toilets than this. When you flush, the cistern has to refill automatically from a kind of faucet on the side and the refilling operation has to last just long enough to fill the tank without making it overflow. The "hole in the ground" is more sophisticated than it looks as well. You may have noticed that toilets always have a little water in the bottom of them; even when you flush them, they never empty completely. Some water is always trapped in a big curved pipe at the base of the toilet known as the S-bend (or S-trap). This little bit of water effectively seals off the sewage pipe beneath it, stopping germs and bad smells from coming up into your bathroom.

Photo: Lift the cistern on a toilet and this is what you'll find inside. The cistern (upper tank of water) drains through a valve in the center through the force of gravity. The blue, balloon-like object on the left is a plastic float that drops when the water level falls. This tilts the plastic lever (known as the ballcock) and allows the cistern to refill.

Further reading

• How Things Work/Flush Toilet: Here's an alternative explanation of flush toilets with some nice cutaway diagrams showing the mechanism inside very clearly.
• The Complete Guide to Plumbing: Our own guide to making water work in your home.