A piped water supply and distribution system is intermittent 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] In Jordan, 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]

• Water scarcity