A water pipe is any pipe or tube designed to transport treated drinking water to consumers. The variants may include large diameter mains pipes which supply entire towns, smaller branch lines which supply a street or group of buildings, or small diameter pipes located within individual buildings. Water pipes range in size from giant mains examples of up to 144 inches (365 cm) in diameter to small 1/2 inch (12.7 mm) pipes used to feed individual outlets within a building. Materials commonly used to construct water pipes include polyvinyl chloride (PVC), copper, steel and, in older systems, concrete or fired clay. Joining individual water pipe lengths to make up extended runs is made possible with flange, nipple, compression or soldered joints.
The supply of fresh drinking water to residential, business, and industrial areas is one of the oldest utility services in history and one that has, since Roman times, depended on the unassuming water pipe for its implementation. Early examples of water pipes were influenced by the technology, or rather lack thereof, of the day and were generally constructed of easily accessible and workable materials such as wood and the lead sheeting used by the Romans. Wooden pipes were often no more than hollowed logs joined together with a rather odious mixture of heated animal fat. Roman lead water pipes were generally square in cross section with folded seams and joints. The use of lead in water pipe construction continued well into the early part of the 20th Century when the health hazards associated with the use of the metal became more clearly understood and with a resultant switch to steel, copper and PVC piping.
Modern water supply networks and installations use water pipes in a number of standard application categories. The first of these is the water main which typically features large diameter steel, concrete, or PVC pipes which bring the water feed into the immediate consumer area. These pipes may range in size from 6 to 144 inches (15–365 mm) in diameter and are typically rated at a minimum working pressure of 30 pounds per square inch (PSI). Most mains systems utilize steel flanges to join individual pipe lengths. Most water mains are subterranean or buried lines although in some cases they may run on the surface supported by concrete pylons.
In the immediate vicinity of consumer points, the water main will feed several smaller water pipe runs which act as a secondary distribution system. These are typically also steel or PVC pipes of an average diameter of 4 to 12 inches (10–30 cm). Individual consumer points branch off from these secondary feeds with steel or PVC piping of approximately 2 inch (5 cm) which then introduce the water to the pipe system in the building. These pipes are most commonly PVC or copper varieties with an average size of 1/2 inch to 1 inch (12.7 to 25.4 mm) and channel the incoming feed to individual water heaters, faucets, and toilets. Most joints on installation water pipes are either compression type fittings in the case of PVC piping or soldered joints on copper piping.