Tap water

Tap water
Indoor Tap - commonly found in the bathroom or kitchen. This tap is a single-handle, double-spout tap (one spout for hot water, one spout for cold water).

Tap water (running water, city water, municipal water, etc.) is a principal component of "indoor plumbing", which became available in urban areas of the developed world during the last quarter of the 19th century, and common during the mid-20th century. The application of technologies involved in providing clean or "potable" water to homes, businesses and public buildings is a major subfield of sanitary engineering.



The availability of tap water has major public health benefits, since it typically vastly reduces the risk to the public of contracting water-borne diseases. 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 wastewater.

Specific chemical compounds are often added to 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.

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.[1]

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

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. 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 during the DWV 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 methods 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, however plastic water pipes do not keep water as clean as copper and brass piping does. Copper pipe plumbing is bacteriostatic. This means that bacteria can't grow in the copper pipes. Plumbing codes define which materials may be used, and all materials must be proven by ASTM, UL, and/or NFPA testing.


Galvanized steel potable water supply and distribution pipes are commonly found with nominal diameters 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, 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. 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 it suffers from a tendency to become obstructed due to internal rusting and mineral deposits forming on the inside of the pipe over time after 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.


See also Copper tubing

Copper Tubing Sizes (CTS) for Plumbing
Outside diameter
[in (mm)]
Inside diameter (ID)
[in (mm)]
Type K Type L Type M
38 12 (12.7) 0.402 (10.211) 0.430 (10.922) 0.450 (11.430)
12 58 (15.875) 0.528 (13.411) 0.545 (13.843) 0.569 (14.453)
58 34 (19.05) 0.652 (16.561) 0.668 (16.967) 0.690 (17.526)
34 78 (22.225) 0.745 (18.923) 0.785 (19.939) 0.811 (20.599)
1 1+18 (28.575) 0.995 (25.273) 1.025 (26.035) 1.055 (26.797)
114 1+38 (34.925) 1.245 (31.623) 1.265 (32.131) 1.291 (32.791)
112 1+58 (41.275) 1.481 (37.617) 1.505 (38.227) 1.527 (38.786)
2 2+18 (53.975) 1.959 (49.759) 1.985 (50.419) 2.009 (51.029)
212 2+58 (66.675) 2.435 (61.849) 2.465 (62.611) 2.495 (63.373)
3 3+18 (79.375) 2.907 (73.838) 2.945 (74.803) 2.981 (75.717)


Common wall-thicknesses of copper tubing in the USA are "Type K", "Type L" and "Type M":[2]

  • Type K has the thickest wall section of the three types of pressure rated tubing and is commonly used for deep underground burial such as under sidewalks and streets, with a suitable corrosion protection coating or continuous polyethylene sleeve as required by code.
  • Type L has a thinner pipe wall section, and is used in residential and commercial water supply and pressure applications.
  • Type M has the thinnest wall section, and is generally suitable for condensate and other drains, but sometimes illegal for pressure applications, depending on local codes.

Types K and L are generally available in both hard drawn "sticks" and in rolls of soft annealed tubing, whereas type M is usually only available in hard drawn "sticks".

In the plumbing trade the size of copper tubing is measured by its nominal diameter (average inside diameter). Some American trades, heating and cooling technicians for instance, use the outside diameter (OD) to designate copper tube sizes. The HVAC tradesman also use this different measurement to try and not confuse water pipe with copper pipe used for the HVAC trade, as pipe used in the air-conditioning trade uses copper pipe that is made at the factory without processing oils that would be incompatible with the oils used to lubricate the compressors in the AC system. The OD of copper tube is 18th inch larger than its nominal size. Therefore, 1 inch nominal copper tube and 1 18th inch ACR tube are exactly the same tube with different size designations. The wall thickness of the tube, as mentioned above, never affects the sizing of the tube. Type K 12 inch nominal tube, is the same size as Type L 12 inch nominal tube (58 inch ACR).

Common wall-thicknesses in Europe are "Type X", "Type Y" and "Type Z", defined by the EN 1057 standard.

  • Type X is the most common, and is used in above groundservices including drinking water supply, hot and cold water systems, sanitation, central heating and other general purpose applications.
  • Type Y is a thicker walled pipe, used for underground works and heavy duty requirements including hot and cold water supply, gas reticulation, sanitary plumbing, heating and general engineering.
  • Type Z is a thinner walled pipe, also used for above groundservices including drinking water supply, hot and cold water systems, sanitation, central heating and other general purpose applications.

In the plumbing trade the size of copper tubing is measured by its outside diameter in millimetres. Common sizes are 15 mm and 22 mm.[3]

Thin-walled types used to be relatively inexpensive, but since 2002 copper prices have risen considerably due to rising global demand and a stagnant supply.

Lead leaching

Generally, copper tubes are soldered directly into copper or brass fittings, although compression, crimp, or flare fittings are also used. Formerly, concerns with copper supply tubes included the lead used in the solder at joints (50% tin and 50% lead). Some studies have shown significant "leaching" of the lead into the potable water stream, particularly after long periods of low usage, followed by peak demand periods. In hard water applications, shortly after installation, the interior of the pipes will be coated with the deposited minerals that had been dissolved in the water, and therefore the vast majority of exposed lead is prevented from entering the potable water. Building codes now require lead-free solder. Building Codes throughout the U.S. require the use of virtually "lead-free" (<.2% lead) solder or filler metals in plumbing fittings and appliances as well.


Copper water tubes are susceptible to: cold water pitting caused by contamination of the pipe interior typically with soldering flux; erosion corrosion caused by high speed or turbulent flow; and stray current corrosion, caused by poor electrical wiring technique, such as improper grounding and bonding.

Pin holes due to poor plumbing electrical grounding and/or bonding

Pin-hole leaks can occur anytime copper piping is improperly grounded and/or bonded; nonmetal piping, such as Pex or PVC, does not suffer from this problem. The phenomenon is known technically as stray current corrosion or electrolytic pitting. Pin-holing due to poor grounding or poor bonding occurs typically in homes where the original plumbing has been modified; homeowners may find a new plastic water filtration device or plastic repair union has interrupted the water pipe's electrical continuity to ground when they start seeing pinhole water leaks after a recent install. Damage occurs rapidly, usually being seen about six months after the ground interruption. Correctly installed plumbing appliances will have a copper bonding jumper cable connecting the interrupted pipe sections. Pinhole leaks from stray current corrosion can result in thousands of dollars in plumbing bills, and sometimes necessitating the replacement of the entire affected line. The cause is an electrical problem, not a plumbing problem; once the plumbing damage is repaired, an electrician should be consulted to evaluate the grounding and bonding of the entire plumbing system.

The difference between a ground and a bond is subtle. See Ground, for a complete description.

Stray current corrosion occurs because: 1) the piping system is connected accidentally or intentionally to a DC voltage source; 2) the piping does not have metal-to-metal electrical continuity; 3) if the voltage source is AC, one or more naturally occurring minerals coating the pipe interior act as a rectifier, converting AC current to DC . The DC voltage forces the water within the piping to act as an electrical conductor (an electrolyte). Electric current leaves the copper pipe, moves though the water across the nonconductive section (the plastic filter housing in the example above), and reenters the pipe on the opposite side. Pitting occurs at the electrically negative side (the cathode), which may be upstream or downstream with respect to the water flow direction. Pitting occurs because the electrical voltage ionizes the pipe's interior copper metal, which reacts chemically with dissolved minerals in the water creating copper salts; these copper salts are soluble in water and wash away. Pits eventually grow and consolidate to form pin holes. Where there is one, there are almost certainly more. A complete discussion of stray current corrosion can be found in chapter 11, section 11.4.3, of Handbook of Corrosion Engineering, by Pierre Roberge.[4]

Detecting and eliminating poor bonding is relatively straightforward. Detection is accomplished by use of a simple voltmeter set to DC with the leads placed in various places in the plumbing. Typically, a probe on a hot pipe and a probe on a cold pipe will tell you if there is improper grounding. Anything beyond a few millivolts is important, potentials of 200 mV are common. A missing bond will show up best in the area of the gap, as potential disperses as the water runs. Since the missing bond is usually seen near the water source, as filtration and treatment equipment are added, pinhole leaks can occur anywhere downstream. It is usually the cold water pipe, as this is the one that gets the treatment devices.

Correcting the problem is a simple matter of either purchasing a copper bonding jumper kit, composed of copper cable at least #6 AWG in diameter and two bronze ground clamps for affixing it the plumbing. See NFPA 70, the U.S. National Electrical Code Handbook (NEC), section on bonding and ground for details on selecting the correct bonding conductor wire size.

A similar bonding jumper wire can also be seen crossing gas meters, but for a different reason.

Note, if homeowners are experiencing shocks or sparks from plumbing fixtures or pipes, it is more than a missing bond, it is likely a live electrical wire is bridging to the plumbing and the plumbing system is not grounded. This is an electrical shock hazard and potential fire danger; consult an electrician immediately!


Plastic piping placed for a sink

Plastic pipe is in wide use for domestic water supply and drainage, waste, and 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 certain 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 for cold water only, or 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,[5] but since the early 1970s has seen increasing use worldwide for both domestic hot and cold water. PP pipes are heat fused, preventing the use of glues, solvents, or mechanical fittings. PP pipe is often used in green building projects.[6][7]
  • 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 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 fittings.
  • Polytanks - plastic polyethylene cisterns, underground water tanks, above ground water tanks, are 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 - aluminum pipe sandwiched between layers of PEX and connected with brass compression fittings. In 2005, a large number of their fittings were recalled.

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.[8][9] 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.

Tap water versus bottled water

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.[10] 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.[11]

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.[12]

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."[13]

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.[14]

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.[15]

Dissolved gases

Tap water can sometimes appear cloudy, and this is often mistaken for a mineral impurity in the water. Cloudy water, also known as white water, is actually 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 with a high dissolved oxygen content that is heated or depressurized, because this reduces how much dissolved gas the water can hold. This condition is completely harmless, and the cloudiness of the water disappears quickly as the gas is released from the water.[16]

See also


  1. ^ Plumbing: the Arteries of Civilization, Modern Marvels video series, The History Channel, AAE-42223, A&E Television, 1996
  2. ^ Copper Tube Handbook, the Copper Development Association, New York, USA, 2006
  3. ^ Pipe sizes
  4. ^ Roberge, P. R. (1999). Handbook of Corrosion Engineering (1st ed.). McGraw-Hill Professional. ISBN 0-07-076516-2. 
  5. ^ http://www.buzzle.com/articles/polypropylene-properties-and-uses.html
  6. ^ http://www.greenbuildingpro.com/resources/whitepapers/1337-one-of-utahs-leeding-residences-full
  7. ^ http://www.pmengineer.com/Articles/Green/2010/06/01/Walking-The-Talk
  8. ^ Uniform Plumbing Code, IAPMO
  9. ^ International Plumbing Code, ICC
  10. ^ [1]
  11. ^ [2]
  12. ^ Washington's Gregoire plans 400 million more in budget cuts, Bloomberg Businessweek, December 16, 2010, http://www.businessweek.com/news/2010-12-16/washington-s-gregoire-plans-400-million-more-in-cuts.html 
  13. ^ [|van der Leun, Justine] (September 2009). "A Closer Look at New Research on Water Safety". AOL Health. http://www.aolhealth.com/healthy-living/pollution-water-effects. Retrieved September 2009. 
  14. ^ 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. 
  15. ^ "Tap Water Quality Analysis"
  16. ^ Massachusetts Water Resource Authority. http://www.mwra.com/04water/2004/whitewater.htm
  • ASTM B75-02 Specification for Seamless Copper Tube
  • ASTM B42-02e1 Standard Specification for Seamless Copper Pipe, Standard Sizes
  • ASTM B88-03 Standard Specification for Seamless Copper Water Tube
  • AWWA Research Foundation, Residential End Uses of Water, ISBN 1-58321-016-4, 1999

External links

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Look at other dictionaries:

  • tap water — tap .water n [U] water that comes out of a ↑tap rather than a bottle …   Dictionary of contemporary English

  • tap water — n. water taken directly from the tap, or faucet, as for drinking or cooking …   English World dictionary

  • tap water — tap ,water noun uncount water that comes out of a FAUCET in a building …   Usage of the words and phrases in modern English

  • tap water — noun water directly from the spigot • Hypernyms: ↑water, ↑H2O * * * noun [noncount] : water that comes through pipes from the public water system * * * ˈtap water [tap water] noun …   Useful english dictionary

  • tap water — N UNCOUNT Tap water is the water that comes out of a tap in a building such as a house or a hotel. He never drinks tap water …   English dictionary

  • tap water — /ˈtæp wɔtə/ (say tap wawtuh) noun the water which comes from a public water reservoir, often chlorinated to purify it and fluoridated for public dental health. Compare bottled water. Also, tapwater, tap water …  

  • tap water — vandentiekio vanduo statusas T sritis ekologija ir aplinkotyra apibrėžtis Pagal tam tikrus reikalavimus apdorotas vanduo, tiekiamas į skirstomąjį tinklą arba švaraus vandens rezervuarą. atitikmenys: angl. faucet water; supply water; tap water vok …   Ekologijos terminų aiškinamasis žodynas

  • tap water — tap′ wa ter n. water obtained via a plumbing system directly from a faucet or tap • Etymology: 1880–85 …   From formal English to slang

  • tap water — water, obtained directly from a faucet or tap, that has not been purified, distilled, or otherwise treated. [1880 85] * * * …   Universalium

  • tap water — noun Date: 1881 water as it comes from a tap (as in a home) …   New Collegiate Dictionary

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