A piped water supply and distribution systemisintermittent when water continuity is for less than 24 hours a day or not on all days of the week.[1][2] During this continuity defining factors are water pressure and equity.[3][4] At least 45 countries have intermittent water supply (IWS) systems.[5] It is contrasted with a continuous or "24/7" water supply, the service standard.[6][7] No system is intentionally designed to be intermittent, but they may become that way because of system overexpansion, leakage and other factors.[8][9] As of 2022, there was no feasible method for modelling IWS, including no computer-aided tools.[1] Contamination issues can be associated with an intermittent water distribution system.[10] Global public health impact includes millions of cases of infections and diarrhea, and 1560 deaths annually.[11]
A continuous supply is not practical in all situations.[3] In the short term, an IWS may have some benefits.[12] These may include addressing demand with a limited supply in a more economical manner.[13] An intermittent supply may be temporary (e.g., when water reserves are low) or permanent (e.g., where the piped system cannot sustain a continuous supply).[6] Associated factors resulting from an intermittent supply include water extraction by users at the same time, resulting in low pressure and a possible higher peak demand.[14]
A large share of water supply systems around the world are intermittent; in other words, intermittent water supply is a norm.[15][16] About 1.3 billion people have a piped supply that is intermittent, including large populations in Africa, Asia, and Latin America.[1][14] This does not include those who do not get piped water at all, about 2.7 billion people.[1] Countries with intermittent supply in some areas and continuous supply in others include India[17] and South Africa.[18] In India, various cities are at various stages of constructing 24/7 supply systems, such as Chandigarh,[19] Delhi,[20] Shimla,[21] and Coimbatore.[22] In Cambodia, Phnom Penh increased coverage from 25% to 85% and duration from 10 to 24 hours a day between 1993 and 2004.[23]
Installation of storage and pumps at residences may offset the intermittency of the water supply.[6] Roof tanks are a common feature in countries where the water supply is intermittent.[24]InJordan, most houses have one or more ground or roof tanks. An intermittent supply can be supplemented with other non-piped sources such as packaged drinking and cooking water bought from local shops or delivered to the house.[25]
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The primary cause of intermittent water supply is the extension of distribution systems beyond their hydraulic capacity to provide service to more customers.
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