A large community cannot use wells to advantage because of the danger of contamination. Therefore, it is necessary to secure water from a distance and allow it to flow to the community. It is therefore pumped to a basin, called a reservoir, which is situated at the highest elevation in the vicinity. At the reservoir there is usually erected a large steel stand-pipe to supply the water to the houses near or on the same level as the reservoir.
Water is pumped to a reservoir to secure a uniform pressure which will force the water to the tops of buildings. As water seeks its own level, it will rise in the buildings to the height of the reservoir. This is called the gravity system of waterworks, as the force that drives the water is the force of gravity. While this system may be used to advantage in some cities, in other cities an elaborate pumping system must be employed.
Water is conducted from the reservoir through broad pipes called mains. Smaller pipes are attached to the mains and run at an angle to the sidewalk. At the edge of the sidewalk there are valves, called hydrants, for shutting off or turning on the water. The pipes enter the houses through the cellars and pass through meters where the volume of water is measured in gallons. Pipes are conducted from the cellars to different rooms. Water is obtained from the pipes by means of valves called faucets.