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Plumbing is the system of pipes, drains fittings, valves, valve assemblies, and devices installed in a building for the distribution of water for drinking, heating and washing, and the removal of waterborne wastes, and the skilled trade of working with pipes, tubing and plumbing fixtures in such systems. A plumber is someone who installs or repairs piping systems, plumbing fixtures and equipment such as water heaters and backflow preventers. The plumbing industry is a basic and substantial part of every developed economy due to the need for clean water, and sanitary collection and transport of wastes. The word "plumbing" comes from the Latin plumbum for lead, as pipes were once made from lead.
Plumbing is usually distinguished from water supply and sewage systems, in that a plumbing system serves one building, while water and sewage systems serve a group of buildings.
Plumbing originated during ancient civilizations such as the Greek, Roman, Persian, Indian, and Chinese cities as they developed public baths and needed to provide potable water and drainage of wastes, for larger numbers of people. Standardized earthen plumbing pipes with broad flanges making use of asphalt for preventing leakages appeared in the urban settlements of the Indus Valley Civilization by 2700 B.C. The Romans used lead pipe inscriptions to prevent water theft.
Improvement in plumbing systems was very slow, with virtually no progress made from the time of the Roman system of aqueducts and lead pipes. Plumbing was extremely rare until the growth of modern densely-populated cities in the 1800s. During this period, public health authorities began pressing for better waste disposal systems to be installed, to prevent or control epidemics of disease. Earlier, the waste disposal system had merely consisted of collecting waste and dumping it on the ground or into a river. Eventually the development of separate, underground water and sewage systems eliminated open sewage ditches and cesspools.
Most large cities today pipe solid wastes to sewage treatment plants in order to separate and partially purify the water, before emptying into streams or other bodies of water. For potable water use, galvanized iron piping was commonplace in the United States from the late 1800s until around 1960. After that period, copper piping took over, first soft copper with flared fittings, then with rigid copper tubing utilizing soldered fittings.
The use of lead for potable water declined sharply after World War II because of increased awareness of the dangers of lead poisoning. At this time, copper piping was introduced as a better and safer alternative to lead pipes.
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Water systems of ancient times relied on gravity for the supply of water, using pipes or channels usually made of clay, lead, bamboo, wood, or stone. Hollowed wooden logs wrapped in steel banding were used for plumbing pipes, particularly water mains. Logs were used for water distribution in England close to 500 years ago. US cities began using hollowed logs in the late 1700s through the 1800s.
Present-day water-supply systems use a network of high-pressure pumps, and pipes in buildings are now made of copper, brass, plastic (particularly cross-linked polyethylene called PEX, which is estimated to be used in 60% of single-family homes), or other nontoxic material. Due to its toxicity, lead has not been used in modern water-supply piping since the 1930s in the United States, although lead was used in plumbing solder for drinking water until it was banned in 1986. Drain and vent lines are made of plastic, steel, cast-iron, or lead.
The straight sections of plumbing systems are called "pipes" or "tubes". A pipe is typically formed via casting or welding, whereas a tube is made through extrusion. Pipe normally has thicker walls and may be threaded or welded, while tubing is thinner-walled and requires special joining techniques such as brazing, compression fitting, crimping, or for plastics, solvent welding. These joining techniques are discussed in more detail in the piping and plumbing fittings article.
Plumbing fixtures are exchangeable devices using water that can be connected to a building's plumbing system. They are considered to be "fixtures", in that they are semi-permanent parts of buildings, not usually owned or maintained separately. Plumbing fixtures are seen by and designed for the end-users. Some examples of fixtures include water closets (also known as toilets), urinals, bidets, showers, bathtubs, utility and kitchen sinks, drinking fountains, ice makers, humidifiers, air washers, fountains, and eye wash stations.
Equipment and tools 
Plumbing equipment includes devices often hidden behind walls or in utility spaces which are not seen by the general public. It includes water meters, pumps, expansion tanks, backflow arrestors, water filters, UV sterilization lights, water softeners, water heaters, heat exchangers, gauges, and control systems.
Specialized plumbing tools include pipe wrenches, flaring pliers, and joining tools such as soldering torches and crimp tools. New tools have been developed to help plumbers fix problems more efficiently. For example, plumbers use video cameras for inspections of hidden leaks or problems, they use hydro jets, and high pressure hydraulic pumps connected to steel cables for trench-less sewer line replacement.
The major categories of plumbing systems or subsystems are:
- Potable cold and hot tap water supply
- Plumbing drainage venting
- Septic systems
- Rainwater, surface, and subsurface water drainage
- Fuel gas piping
For their environmental benefit and sizable energy savings, hot water heat recycling units are being installed in residential buildings. Ecological concerns and water shortages have increased interest in graywater recovery and treatment systems.
Plumbing may also include hydronics, which involves heating and cooling systems utilizing water to transport thermal energy. The New York City steam system is an example of a large district heating system.
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Fire protection systems are largely used in commercial and residential buildings, and they may be a very simple system or an integrated solution which, beyond fire sensors and fire extinguishers methods based on spraying or sprinkling fire-suppressing fluids, includes the use of materials that have high fire-resistance coefficients to delay fire propagation. These materials and their use are regulated by specific standards that, not only manufacturers use in the fabrication process (flame retardant electric cables, for example), but also service providers in systems implementations and assemblies in the field.
Sometimes, a tube or another mechanical part has to penetrate a wall or floor that has special fire insulation material or that have special fire insulation resistance, it is needed to recover the original level of security of the fire system in case of maintenance, or to reach the designed level of security, so to avoid or delay the propagation of flame, smoke and heat accordingly.
Firestopping is a technique used in these cases, and it is required where mechanical penetrants traverse fire-resistance rated wall and floor assemblies, or membranes thereof. This work is usually done worldwide by the insulation trade and/or specialty firestop sub-contractors.
Much of the plumbing work in populated areas is regulated by government or quasi-government agencies due to the direct impact on the public's health, safety, and welfare. Plumbing installation and repair work on residences and other buildings generally must be done according to plumbing and building codes to protect the inhabitants of the buildings and to ensure safe, quality construction to future buyers. If permits are required for work, plumbing contractors typically secure them from the authorities on behalf of home or building owners.
In the United Kingdom the professional body is the Chartered Institute of Plumbing and Heating Engineering (educational charity status) and it is true that the trade still remains virtually ungoverned; there are no systems in place to monitor or control the activities of unqualified plumbers or those home owners who choose to undertake installation and maintenance works themselves, despite the health and safety issues which arise from such works when they are undertaken incorrectly; see Health Aspects of Plumbing (HAP) published jointly by the World Health Organization (WHO) and the World Plumbing Council (WPC). WPC has subsequently appointed a representative to the World Health Organization to take forward various projects related to Health Aspects of Plumbing.
See also 
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- Plumbing: the Arteries of Civilization, Modern Marvels video series, The History Channel, AAE-42223, A&E Television, 1996
- Teresi et al. 2002
- Kavanaugh, Sean. "History of Plumbing Pipe and Plumbing Material".
- Copper Tube Handbook, the Copper Development Association, New York, USA, 2006
- California’s PEX Battle Continues. Builderonline.com
- Macek, MD.; Matte, TD.; Sinks, T.; Malvitz, DM. (Jan 2006). "Blood lead concentrations in children and method of water fluoridation in the United States, 1988-1994.". Environ Health Perspect 114 (1): 130–4. doi:10.1289/ehp.8319. PMC 1332668. PMID 16393670. More than one of
- Uniform Plumbing Code, IAPMO
- International Plumbing Code, ICC
- "Lead Pipe History". Retrieved 2010-01-12.
- "Home =CIPHE". Retrieved 2009-10-11.
- "WHO Health aspects of plumbing". Retrieved 2009-10-11.
Further reading 
- Teresi, Dick; et al. (2002). Lost Discoveries: The Ancient Roots of Modern Science--from the Babylonians to the Maya. New York: Simon & Schuster. pp. 351–352. ISBN 0-684-83718-8.