) is part of indoor plumbing
, which became available in the late 19th century and common in the mid-20th century.
The provision of tap water requires a massive infrastructure of piping, pumps, and water purification works. The direct cost of the tap water alone, however, is a small fraction of that of bottled water, which can cost from 240 to 10,000 times as much per gallon.
Experimental attempts have been made to introduce non-potable greywater or rainwater for these secondary uses in order to reduce enormous environmental and energy costs. In urban China, drinking water can be optionally delivered by a separate tap.
The availability of clean tap water brings major public health benefits. Usually, the same administration that provides tap water is also responsible for the removal and treatment before
discharge or reclamation of wastewater.
In many areas, chemicals containing fluoride are added to the tap water in an effort to improve public dental health. This remains a controversial issue in the health, freedoms and rights of the individual. See water fluoridation controversy.
Tap water may contain various types of natural but relatively harmless contaminants such as scaling agents like calcium carbonate in hard water and metal ions such as magnesium and iron, and odoriferous gases such as hydrogen sulfide. Local geological conditions affecting groundwater are determining factors of the presence of these substances in water.
Occasionally, there are health scares concerning the leakage of dangerous biological or chemical contaminating agents into local water supplies when people are advised by public health officials not to drink the water, and stick to bottled water instead. An example is the recent discovery of potentially hazardous nitrates in the public water supply in Phoenix, Arizona.
Tap water uses
According to a 1999 American Water Works Association
study on residential
end uses of water in the United States, Americans drink more than 1 glass of tap water per day (the daily human drinking water
requirement being 2-3 quarts
). Daily indoor per capita water use in a typical single family home is 69.3 gallons
), falling into the following categories:
Of all water supplied to studied homes annually, for perspective, 42 percent was for indoor purposes and 58 percent for outdoor purposes.
Potable water supply
This supply may come from several possible sources.
Domestic water systems have been evolving since the first thinking man located his home near a running water supply, e.g. a stream or river. The water flow also allowed sending waste water away from his domicile.
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.
Fixtures are devices that use water without an additional source of power.
Appliances are devices that use water coupled with an additional source of power. connection to these appliances incorporates a backflow prevention principle of some form -- 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.
In old construction, lead plumbing
was common. It was generally eclipsed toward the end of the 1800s by galvanized iron water pipes
which were attached with threaded pipe fittings
. Higher durability, and cost, systems were made with brass
pipe and fittings. Copper
fittings became popular around 1950, though it had been used as early as 1900. Plastic supply pipes have become increasingly common since about 1970, with a variety of materials and fittings employed. Plumbing codes
define which materials may be used, and all materials must be proven by ASTM, UL, and/or NFPA testing.
are commonly found with interior diameters from 1/2" to 2", though most single family homes' systems won't require any supply pipes larger than 3/4". Pipes have National Pipe Thread
(NPT) standard male threads, which connect with female 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
, and suffers from a tendency to obstruction due to mineral deposits forming on the inside of the pipe. It remains common 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
Copper Tubing Sizes (CTS) for Plumbing
| Outside diameter (OD)|
| Inside diameter (ID)|
||Type M |
|| 0.450 |
|| 0.569 |
|| 0.690 |
|| 0.811 |
|| 1.055 |
|| 1.291 |
|| 1.527 |
|| 2.009 |
|| 2.495 |
|| 2.981 |
made of copper
was introduced in about 1900, but didn't become popular until approximately 1950, depending on local building code adoption. Common wall-thicknesses of copper tubing are "Type K", "Type L" and "Type M"; Type "M" are relatively thin-walled and generally suitable for condensate and other drains, but sometimes illegal for pressure applications, depending on local codes. Type "L" has a thicker pipe wall section, and is used in residential and commercial water supply and pressure applications, 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. Types "K" and "L" are generally available in both hard drawn "sticks" and in rolls of soft annealed tubing, Type "M" is usually only available in hard drawn "sticks". 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.
In the plumbing trade the size of copper tubing is measured by its nominal diameter (average inside diameter). Some trades, heating and cooling technicians for instance, use the outside diameter (OD) to designate copper tube sizes. The OD of copper tube is always 1/8th inch larger than its nominal size. Therefore, 1" nominal copper tube and 1-1/8th" 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 1/2" nominal tube, is the same size as Type L 1/2" nominal tube (5/8" ACR).
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.
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), polybutlyene (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.
- PBT - flexible (usually gray or blue) 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
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 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.
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 vs bottled water
Tap water is an alternative to bottled water, and is preferred by many Americans because their water wholesalers and water companies claim to provide relatively clean and healthy water to consumers.
In 2007, it was found that some bottled water companies were selling water that was contaminated and less healthy for consumers than tap water. The Natural Resources Defense Council
(NRDC) conducted a four year study on bottled water. The results of this study show that one-third of the bottled water tested contained levels of contamination which exceeds allowable limits under either state or bottled water industry standards or guidelines.
Many large corporations and some water companies and wholesalers, especially in the California Bay Area are now making a large effort to promote tap water over bottled water. Some of the Bay Area cities that promote tap over bottled water include San Francisco, Emeryville, Santa Clara, and Oakland. The Santa Clara Valley Water District in Santa Clara County launched its tap v bottled water campaign, with the slogan, “Tap Water, the Clear Choice”, in 2007.
During the 2007 U.S Conference of Mayors, the mayors of San Francisco, Salt Lake City and Minneapolis signed a pledge to promote tap water over bottled water as part of the “Think Outside the Bottle” campaign.
- 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