The craft of plumbing originated in medieval times when the roofs of the great cathedrals throughout Europe were being covered in sheet lead which had been cast on a bed of sand. Later, when the water supply industry was developing, pipes and cisterns were made from similar cast lead sheet, although hundreds of years before that the Romans had made water pipes of lead to feed their fountains and baths.
Today the modern plumber embraces many skills and materials: cold and hot water supply, sanitation and the installation of pipelines in all types of buildings, for carrying liquids and gases. The plumber has to be able to work in lead, copper, aluminum, cast iron, steel, and plastics.
It is the task of the water industry to supply pure potable water in sufficient quantity wherever it is needed; it is then the job of the plumber to insure that the water is conveyed to all parts of the building where it is required and to preserve its purity up to the point of use. Since careful design and choice of materials are necessary to prevent the water from becoming polluted, there are regulations and laws which must be adhered to.
Because of geographical and physical differences, cold water installations vary from country to country, but in the U.S. one system is most common. Clean fresh water is directed around the community by a system of water pipes buried under the roads. The water running through the pipes is under pressure and is taken into each building by a service pipe. The service pipe is connected directly to the water meter, which registers the amount of water used in each installation for the purpose of billing by the water utility. Just beyond the water meter is a main valve which will halt the flow of water through the building in an emergency. The cold water, which is supplied under pressure usually be;ween 40 and 50 psi (2.8 – 3.35 kg/cm2), is directed to all the cold water faucets and the other fixtures by a network of branch pipes of varying dimensions. The largest is usually 0.75 in. (19 mm) in diameter and ;he smallest – used in flexible tubing connecting a toilet faucet – is 0.375 in. (9.5 mm) in diameter. There are usually shutoff valves fitted near each fixture and faucet to allow them to be isolated for individual repairs.