water supply water supply water supply is the provision of water by public utilities, commercial organisations, community endeavors or by individuals, usually via a system of pumps and pipes. public water supply systems are crucial to properly functioning societies. these systems are what supply drinking water to populations around the globe. aspects of service quality include continuity of supply, water quality and water pressure. the institutional responsibility for water supply is arranged differently in different countries and regions (urban versus rural). it usually includes issues surrounding policy and regulation, service provision and standardization. a girl collects clean water from a communal water supply in kawempe, uganda. the cost of supplying water consists, to a very large extent, of fixed costs (capital costs and personnel costs) and only to a small extent of variable costs that depend on the amount of water consumed (mainly energy and chemicals). almost all service providers in the world charge tariffs to recover part of their costs. water supply is a separate topic from irrigation, the practice and systems of water supply on a larger scale, for a wider variety of purposes, primarily agriculture. technical overview further information: water supply network, water treatment, and water distribution system engine room of municipal water works in toledo, ohio, 1908 water supply systems get water from a variety of locations after appropriate treatment, including groundwater (aquifers), surface water (lakes and rivers), and the sea through desalination. the water treatment steps include, in most cases, purification, disinfection through chlorination and sometimes fluoridation. treated water then either flows by gravity or is pumped to reservoirs, which can be elevated such as water towers or on the ground (for indicators related to the efficiency of drinking water distribution see non-revenue water). once water is used, wastewater is typically discharged in a sewer system and treated in a sewage treatment plant before being discharged into a river, lake, or the sea or reused for landscaping or irrigation. use in the united states, the typical single family home uses about 520 l (138 us gal) of water per day (2016 estimate) or 222 l (58.6 us gal) per capita per day. this includes several common residential end use purposes (in decreasing order) like toilet use, showers, tap (faucet) use, washing machine use, leaks, other (unidentified), baths, and dishwasher use. trends during the beginning of the 21st century, especially in areas of urban and suburban population centers, traditional centralized infrastructure have not been able to supply sufficient quantities of water to keep up with growing demand. among several options that have been managed are the extensive use of desalination technology, this is especially prevalent in coastal areas and in "dry" countries like australia. decentralization of water infrastructure has grown extensively as a viable solution including rainwater harvesting and stormwater harvesting where policies are eventually tending towards a more rational use and sourcing of water incorporation concepts such as "fit for purpose". service quality water supply service quality has many dimensions: continuity; water quality; pressure; and the degree of responsiveness of service providers to customer complaints. many people in developing countries receive a poor or very poor quality of service. water quality is also dependant of the quality and level of pollution of the water source. continuity of supply continuity of water supply is taken for granted in most developed countries, but is a severe problem in many developing countries, where sometimes water is only provided for a few hours every day or a few days a week, that is it is intermittent. this is especially problematic for informal settlements who are often poorly connected to the water supply network and who have no means of procuring alternative sources such as private boreholes. it is estimated that about half of the population of developing countries receives water on an intermittent basis. water quality drinking water quality has a micro-biological and a physico-chemical dimension. there are thousands of parameters of water quality. in public water supply systems water should, at a minimum, be disinfected—most commonly through the use of chlorination or the use of ultraviolet light—or it may need to undergo treatment, especially in the case of surface water. for more details, please see the separate entries on water quality, water treatment and drinking water. water pressure 1880s model of pumping engine, in herne bay museum water pressures vary in different locations of a distribution system. water mains below the street may operate at higher pressures, with a pressure reducer located at each point where the water enters a building or a house. in poorly managed systems, water pressure can be so low as to result only in a trickle of water or so high that it leads to damage to plumbing fixtures and waste of water. pressure in an urban water system is typically maintained either by a pressurised water tank serving an urban area, by pumping the water up into a water tower and relying on gravity to maintain a constant pressure in the system or solely by pumps at the water treatment plant and repeater pumping stations. typical uk pressures are 4–5 bar (60–70 psi) for an urban supply. however, some people can get over eight bars or below one bar. a single iron main pipe may cross a deep valley, it will have the same nominal pressure, however each consumer will get a bit more or less because of the hydrostatic pressure (about 1 bar/10 m height). so people at the bottom of a 30-metre (100 ft) hill will get about 3 bars more than those at the top. the effective pressure also varies because of the pressure loss due to supply resistance even for the same static pressure. an urban consumer may have 5 metres of 15 mm pipe running from the iron main, so the kitchen tap flow will be fairly unrestricted, so high flow. a rural consumer may have a kilometre of rusted and limed 22 mm iron pipe, so their kitchen tap flow will be small. for this reason, the uk domestic water system has traditionally (prior to 1989) employed a "cistern feed" system, where the incoming supply is connected to the kitchen sink and also a header/storage tank in the attic. water can dribble into this tank through a 12 mm pipe, plus ball valve, and then supply the house on 22 or 28 mm pipes. gravity water has a small pressure (say 1⁄4 bar in the bathroom) so needs wide pipes to allow for higher flows. this is fine for baths and toilets but is frequently inadequate for showers. a booster pump or a hydrophore is installed to increase and maintain pressure. for this reason urban houses are increasingly using mains pressure boilers ("combies") which take a long time to fill a bath but suit the high back pressure of a shower. institutional responsibility and governance a great variety of institutions have responsibilities in water supply. a basic distinction is between institutions responsible for policy and regulation on the one hand; and institutions in charge of providing services on the other hand. policy and regulation cape town water crisis warning, july 2018 water supply policies and regulation are usually defined by one or several ministries, in consultation with the legislative branch. in the united states the united states environmental protection agency, whose administrator reports directly to the president, is responsible for water and sanitation policy and standard setting within the executive branch. in other countries responsibility for sector policy is entrusted to a ministry of environment (such as in mexico and colombia), to a ministry of health (such as in panama, honduras and uruguay), a ministry of public works (such as in ecuador and haiti), a ministry of economy (such as in german states) or a ministry of energy (such as in iran). a few countries, such as jordan and bolivia, even have a ministry of water. often several ministries share responsibilities for water supply. in the european union, important policy functions have been entrusted to the supranational level. policy and regulatory functions include the setting of tariff rules and the approval of tariff increases; setting, monitoring and enforcing norms for quality of service and environmental protection; benchmarking the performance of service providers; and reforms in the structure of institutions responsible for service provision. the distinction between policy functions and regulatory functions is not always clear-cut. in some countries they are both entrusted to ministries, but in others regulatory functions are entrusted to agencies that are separate from ministries. regulatory agencies dozens of countries around the world have established regulatory agencies for infrastructure services, including often water supply and sanitation, in order to better protect consumers and to improve efficiency. regulatory agencies can be entrusted with a variety of responsibilities, including in particular the approval of tariff increases and the management of sector information systems, including benchmarking systems. sometimes they also have a mandate to settle complaints by consumers that have not been dealt with satisfactorily by service providers. these specialized entities are expected to be more competent and objective in regulating service providers than departments of government ministries. regulatory agencies are supposed to be autonomous from the executive branch of government, but in many countries have often not been able to exercise a great degree of autonomy. in the united states regulatory agencies for utilities have existed for almost a century at the level of states, and in canada at the level of provinces. in both countries they cover several infrastructure sectors. in many u.s. states they are called public utility commissions. for england and wales, a regulatory agency for water (ofwat) was created as part of the privatization of the water industry in 1989. in many developing countries, water regulatory agencies were created during the 1990s in parallel with efforts at increasing private sector participation. (for more details on regulatory agencies in latin america, for example, please see water and sanitation in latin america and the regional association of water regulatory agencies aderasa.) many countries do not have regulatory agencies for water. in these countries service providers are regulated directly by local government, or the national government. this is, for example, the case in the countries of continental europe, in china and india. service provision water supply service providers, which are often utilities, differ from each other in terms of their geographical coverage relative to administrative boundaries; their sectoral coverage; their ownership structure; and their governance arrangements. geographical coverage the sole water supply of this section of wilder, tennessee, 1942 many water utilities provide services in a single city, town or municipality. however, in many countries municipalities have associated in regional or inter-municipal or multi-jurisdictional utilities to benefit from economies of scale. in the united states these can take the form of special-purpose districts which may have independent taxing authority. an example of a multi-jurisdictional water utility in the united states is wasa, a utility serving washington, d.c. and various localities in the state of maryland. multi-jurisdictional utilities are also common in germany, where they are known as "zweckverbaende", in france and in italy. in some federal countries, there are water service providers covering most or all cities and towns in an entire state, such as in all states of brazil and some states in mexico (see water supply and sanitation in mexico). in england and wales, water supply and sewerage is supplied almost entirely through ten regional companies. some smaller countries, especially developed countries, have established service providers that cover the entire country or at least most of its cities and major towns. such national service providers are especially prevalent in west africa and central america, but also exist, for example, in tunisia, jordan and uruguay (see also water supply and sanitation in uruguay). in rural areas, where about half the world population lives, water services are often not provided by utilities, but by community-based organizations which usually cover one or sometimes several villages. sector coverage some water utilities provide only water supply services, while sewerage is under the responsibility of a different entity. this is for example the case in tunisia. however, in most cases water utilities also provide sewer and sewage treatment services. in some cities or countries utilities also distribute electricity. in a few cases such multi-utilities also collect solid waste and provide local telephone services. an example of