Tap water (running water, city water, municipal water, etc.) is potable water supplied to a tap (valve) inside the household or workplace. It is a principal component of "outdoor plumbing", which became available in suburban areas of the developed world during the last half of the 19th century, and common during the mid-20th century. The application of technologies involved in providing clean (potable) water to homes, businesses and public buildings is a major subfield of sanitary engineering. Calling potable water "tap water" distinguishes it from the other main types of potable water, such as water from rainwater-collecting cisterns, from village pumps (town pumps), or from streams, rivers, or lakes (whose potability varies).
Publicly available treated water has historically been associated with major increases in life expectancy and improved public health. Water-borne diseases are vastly reduced by proper sewage and fresh water availability. Providing tap water to large urban or suburban populations requires a complex and carefully designed system of collection, storage, treatment and distribution, and is commonly the responsibility of a government agency, often the same agency responsible for the removal and treatment of clean water.
Specific chemical compounds are often taken out of tap water during the treatment process to adjust the pH or remove contaminants, as well as chlorine to kill biological toxins. Local geological conditions affecting groundwater are determining factors for the presence of various metal ions, often rendering the water "soft" or "hard".
Tap water remains susceptible to biological or chemical contamination. In the event of contamination deemed dangerous to public health, government officials typically issue an advisory regarding water consumption. In the case of biological contamination, residents are usually advised to boil their water before consumption or to use bottled water as an alternative. In the case of chemical contamination, residents may be advised to refrain from consuming tap water entirely until the matter is resolved.
In many areas a compound of fluoride is added to tap water in an effort to improve dental health among the public. In some communities "fluoridation" remains a controversial issue. (See water fluoridation controversy.)
Potable water supply 
This supply may come from several possible sources.
- Municipal water supply
- Water wells
- Processed water from creeks, streams, rivers, lakes, rainwater, etc.
Domestic water systems have been evolving since people first located their homes near a running water supply, e.g., a stream or river. The water flow also allowed sending waste water away from the domiciles.
Modern indoor plumbing delivers clean, safe, potable water to each service point in the distribution system. It is imperative that the clean water not be contaminated by the waste water (disposal) side of the process system. Historically, this contamination of drinking water has been the largest killer of humans.
Hot water supply 
Domestic hot water is provided by means of water heater appliances, or through district heating. The hot water from these units is then piped to the various fixtures and appliances that require hot water, such as lavatories, sinks, bathtubs, showers, washing machines, and dishwashers.
Fixtures and appliances 
Everything in a building that uses water falls under one of two categories; Fixture or Appliance. As the consumption points above perform their function, most produce waste/sewage components that will require removal by the waste/sewage side of the system. The minimum is an air gap. See cross connection control & backflow prevention for an overview of backflow prevention methods and devices currently in use, both through the use of mechanical and physical principles.
Fixtures are devices that use water without an additional source of power.
Pipe materials 
||It has been suggested that this article be merged into Plumbing. (Discuss) Proposed since March 2012.|
The earliest known evidence of drain tile being used for plumbing was found in Mesopotamia and is estimated to have been made around 3000 BC. The tiles were made from clay mixed with short lengths of straw. Both brass and copper pipes have been found in Egypt believed to have been made close to 2500 BC. The Romans made extensive use of lead pipe by joining sheets of lead into piping to carry their water supply and waste.
During the Dark Ages following the fall of the Roman Empire, plumbing development virtually ceased for centuries except for isolated cases of plumbing installed in palaces and castles. In the 13th century, blacksmiths formed sheets of iron and lap welded the seam to create iron pipe. Though it is unclear as to when galvanized iron pipe was first used, a French chemist named Melouin is credited with developing the process in 1742. The earliest known use for cast iron pipe is for the water supply to a fountain in Langensalza, Germany, built around 1560. In 1819 the first cast iron pipe constructed in the US, was manufactured in Weymouth, New Jersey. Before that time, cast iron pipe and fittings had to be imported from Europe. It was not until the 1960s that the hubless cast iron pipe was brought to the U.S. from Europe by way of Canada.
During the early 1900s, heavy-walled copper joined with threaded fittings was in use, but limited to public buildings because of its high cost. However, during the 1930s light-gauge Copper tube and fittings were developed which made copper economically feasible and increased its popularity. Copper plumbing is bacteriostatic, which means that bacteria can't easily grow in copper pipes.
Polyvinyl chloride (PVC) was produced experimentally in the 19th century but did not become practical to manufacture until 1926, when Waldo Semon of BF Goodrich Co. developed a method to plasticize PVC, making it easier to process. PVC pipe began to be manufactured in the 1940s and was in wide use for Drain-Waste-Vent piping during the reconstruction of Germany and Japan following WWII. In the 1950s, plastics manufacturers in Western Europe and Japan began producing acrylonitrile butadiene styrene (ABS) pipe. The method for producing cross-linked polyethylene (PEX) was also developed in the 1950s. Plastic supply pipes have become increasingly common, with a variety of materials and fittings employed.
Galvanized steel potable water supply and distribution pipes are commonly found with nominal pipe sizes from 3/8 to 2. It is rarely used today for new construction residential plumbing. Steel pipe has National Pipe Thread (NPT) standard tapered male threads, which connect with female tapered threads on elbows, tees, couplers, valves, and other fittings. Galvanized steel (often known simply as "galv" or "iron" in the plumbing trade) is relatively expensive, and difficult to work with due to weight and requirement of a pipe threader. It remains in common use for repair of existing "galv" systems and to satisfy building code non-combustibility requirements typically found in hotels, apartment buildings and other commercial applications. It is also extremely durable and resistant to mechanical abuse. Black lacquered steel pipe is the most widely used pipe material for fire sprinklers and natural gas.
Most single family homes' systems typically won't require supply piping larger than 3/4". In addition to expense, another downside is that steel pipe suffers from a tendency to become obstructed due to internal rusting and mineral deposits forming on the inside of the pipe over time, once the internal galvanizing zinc coating has degraded. In potable water distribution service, galvanized steel pipe has a service life of about 30 to 50 years, although it is not uncommon for it to be less in geographic areas with corrosive water contaminants.
Copper pipe and tubing was widely used for domestic water systems in the later half of the twentieth century. In the early twenty-first century, the rising price of copper drove a shift to plastic pipes for new construction.
Plastic pipe is in wide use for domestic water supply and drain-waste-vent (DWV) pipe. For example, polyvinyl chloride (PVC), chlorinated polyvinyl chloride (CPVC), polypropylene (PP), polybutylene (PB), and polyethylene (PE) may be allowed by code for specific uses. Some examples of plastics in water supply systems are:
- PVC/CPVC - rigid plastic pipes similar to PVC drain pipes but with thicker walls to deal with municipal water pressure, introduced around 1970. PVC should be used only for cold water, or for venting. CPVC can be used for hot and cold potable water supply. Connections are made with primers and solvent cements as required by code.
- PP - The material is used primarily in housewares, food packaging, and clinical equipment, but since the early 1970s has seen increasing use worldwide for both domestic hot and cold water. PP pipes are heat fused, being unsuitable for the use of glues, solvents, or mechanical fittings. PP pipe is often used in green building projects.
- PBT - flexible (usually gray or black) plastic pipe which is attached to barbed fittings and secured in place with a copper crimp ring. The primary manufacturer of PBT tubing and fittings was driven into bankruptcy by a class-action lawsuit over failures of this system. However, PB and PBT tubing has since returned to the market and codes, typically first for "exposed locations" such as risers.
- PEX - cross-linked polyethylene system with mechanically joined fittings employing barbs, and crimped steel or copper rings.
- Polytanks - plastic polyethylene cisterns, underground water tanks, above ground water tanks, are usually made of linear polyethylene suitable as a potable water storage tank, provided in white, black or green, approved by NSF and made of FDA approved materials.
- Aqua - known as PEX-Al-PEX, for its PEX/aluminum sandwich, consisting of aluminum pipe sandwiched between layers of PEX, and connected with modified brass compression fittings. In 2005, a large number of these fittings were recalled.[further explanation needed]
Fittings and valves 
Potable water supply systems require not only pipe, but also many fittings and valves which add considerably to their functionality as well as cost. The Piping and plumbing fittings and Valves articles discuss them further.
Regulation and compliance 
Before a water supply system is constructed or modified, the designer and contractor need to consult the local plumbing code and obtain a building permits prior to construction. Even replacing an existing water heater may require a permit and inspection of the work. NSF 61 is the U.S. national standard for potable water piping guidelines. National and local fire codes should be integrated in the design phase of the water system too to prevent "failure comply with regulations" notices. Some areas of the United States require on-site water reserves of potable and fire water by law.
Waste water 
The waste water from the various appliances, fixtures, and taps is transferred to the waste and sewage removal system via the sewage drain system. This system consists of larger diameter piping, water traps, and is well vented to prevent toxic gases from entering the living space. The plumbing drains and vents article discusses the topic further, and introduces sewage treatment.
Water flow reduction/saving water 
The amount of water that is running though the tap can easily reduced by help of small plastic water flow reducers (reduction between 15 - 50%). These flow reducers are cheap, they save money and reduce the amount of fresh water that is lost into the sink.
Comparison to bottled water 
||The examples and perspective in this section may not represent a worldwide view of the subject. (April 2010)|
In modern Western society, levels of contaminants found in tap water vary for every household and plumbing system. A general conception regarding water is that bottled water is designed to be 'cleaner' than conventional tap water. However, in 1999, The Natural Resources Defense Council (NRDC) released controversial findings from a four year study on bottled water. The results of this study claimed that one-third of the waters tested contained levels of contamination—including synthetic organic chemicals, bacteria, and arsenic—in at least one sample that exceeded allowable limits under either state or bottled water industry standards or guidelines. However, the bottled water industry was quick to dispute the claim saying bottled water is one the most highly regulated food products under the FDA regulatory authority and that the FDA system worked extremely well when coupled with the International Bottled Water Association's Model Code and unannounced inspections.
Some municipalities in the United States are making an effort to use tap water over bottled water on government properties and events. However, others voted the idea down, including voters in the state of Washington who repealed a bottled water tax via citizen initiative.
James Workman, author of the book Heart of Dryness: How the Last Bushmen Can Help Us Endure the Coming Age of Permanent Drought and co-founder of SmartMarkets says that he doesn't believe that "tap water is bad and bottled water is good". Rather he cites differences in quality regulations and standards. "Bottled water is often tap water put through another filter and not held to the same quality regulations as public utility water is."
Chlorine is a disinfectant which is added to tap water in the United States. Chlorine can leave organic material like trihalomethanes and haloacetic acids in the water. The level of chlorine found is small, 1L of chlorinated water gives 0.2 mg of chlorine, which is too small to cause any health problems.
While most U.S. cities have what is considered safe tap water, contaminants ranging from bacteria to heavy metals are present in some tap water and violations of tap water standards have been well-publicized, such as the severe 1993 Cryptosporidium outbreak in Milwaukee, Wisconsin, which led to several deaths and around 400,000 illnesses (see: Milwaukee Cryptosporidium outbreak). The University of Cincinnati recently completed a Tap Water Quality Analysis, funded by PUR, for major US cities.
Cloudiness due to dissolved gases 
Tap water can sometimes appear cloudy, and this is often mistaken for a mineral impurity in the water. Cloudy water is usually caused by air bubbles coming out of solution in the water. Because cold water holds more air than warm water, small bubbles will appear in water. It has a high dissolved oxygen content that is heated or depressurized, which reduces how much dissolved gas the water can hold. The harmless cloudiness of the water disappears quickly as the gas is released from the water.
See also 
- Plumbing: the Arteries of Civilization, Modern Marvels video series, The History Channel, AAE-42223, A&E Television, 1996
- Uniform Plumbing Code, IAPMO
- International Plumbing Code, ICC
- Washington's Gregoire plans 400 million more in budget cuts, Bloomberg Businessweek, December 16, 2010
- [der Leun, Justine] (September 2009). "A Closer Look at New Research on Water Safety". AOL Health. Retrieved September 2009.
- Petraccia, L., Liberati, G., Masciullo S.G., Grassi, M. & Fraioli, A. "Water, mineral waters and health". Clinical Nutrition 25 (3): 377–385. doi:10.1016/j.clnu.2005.10.002.
- "Tap Water Quality Analysis"
- Massachusetts Water Resource Authority. http://www.mwra.com/04water/2004/whitewater.htm
- The Water Information Center - An online resource for public water system basics and water management issues from the National Academy of Sciences.
- US Environmental Protection Agency Drinking water page
- U.S. Centers for Disease Control and Prevention (CDC) Healthy Water - Public Water Systems - One-stop resource for information on public water systems supplying tap water including information on drinking water, fluoridation, water testing, water-related diseases and contaminants, etc., plus links to EPA, WHO, and other resources.
- Bottled Water: Better than the Tap?[dead link] - A Food and Drug Administration site, explains different sources & treatment of water in depth and compares them.
- the International Code Council
- the American Society for Testing and Materials
- the National Ground Water Association
- The Copper Development Association
- 2008 Municipal Water Pricing Report(Canada)
- Notes on Pipe—Copper Pipe weights and max PSI