780 million people in the world lack access to an improved water supply (UNICEF and the WHO, 2012); millions more who have piped water, considered the best type of an improved water supply, may not have safe and reliable water if it is provided intermittently.
Intermittent water supply is when water is available to people from a piped water distribution system for only a limited amount of time. This means that if you live in a place with intermittent water supply and turn on a tap to get a glass of water, take a shower, or wash a dish, no water will come out for many hours of the day or many days of the week.
Water distribution systems that supply water intermittently are designed and constructed for continuous supply; however, in intermittent supply, pipes are empty for hours or days at a time. Usually, a valve operator turns on and off a valve to supply water periodically. In many smaller cities and towns with intermittent supply, the water utility will supply water to everyone at the same time. In larger cities, they may supply it rotationally throughout the city; one family will get water for two hours, their neighbors a few streets away will get water several hours later, and families living on the other side of the city may get water the next day. [photo of turning on a valve]
Intermittent piped water supply is common in towns and cities in Asia, Africa, and Latin America. While there is not much data about how common it is, the World Health Organization/UNICEF Joint Monitoring Program, which tracks statistics related to water and sanitation throughout the world, estimates that 90% of urban residents in South Asia and 30% in each of Latin America and Africa have intermittent water supply (WHO and UNICEF, 2000). The World Bank's International Benchmarking Networking , which collects data on water utilities, report that 84% of reporting utilities in low-income and 14% in middle-income countries supply for fewer than 24 hours of the day (van den Berg and Danilenko, 2011). India has some of the fewest hours of supply in the world: no major city in India has continuous water supply, and most report an availability of 4 hours per day (McKenzie and Ray, 2009).
Intermittent supply creates problems for both the water utility and households who need to use the water. Since water is not always available, households must store water between delivery times. The amount they need to store depends on the number of people in the house, the amount of water they require, and time until water will be delivered again. A family of 6 using 50 liters/person/day (intermediate water access, defined by the World Health Organization (Howard and Bartram, 2003)) would need to store 300 liters (80 gallons) water for a day. A larger household of 10 people that receives water every five days would need to store at least 2500 liters (660 gallons). If households cannot store that much water, or they run out of water, they may need to turn to other water sources, such as groundwater, which in a city is likely polluted, or pay a much higher cost for vended or tanker truck water. The extra costs that households must pay to cope with unreliable access to water – storage containers, alternative sources, pumping costs, labor - are known as coping costs, and often add up to more than the amount they pay to the utility for the water (Dutta and Tiwari, 2005).
Intermittent supply can also create problems for the water utilities, as it is difficult to track where the water is going (and therefore track down and fix leaks in the distribution system) and to collect payments from consumers who may be unhappy with unreliable water. Intermittent supply can also create problems for water quality, as contamination from outside a pipe can enter through cracks in the pipe when they are empty (Lee and Schwab 2005; Coelho et al 2003; Tokajian and Hashwa 2003).
A distribution system is made up not only of pipes, but also of valve, pumps, tanks, reservoirs, and many other components (Jesperson, 2001). Any problem with a piece of the distribution system – such as a pipe breaking, electricity going out, or human error - will affect the ability of water to flow through. It is complicated for the sometimes hundreds of utility employees to coordinate where water is flowing at any time, if there are problems to fix, and to time turning on and off the complicated network of valves. This means a house may not know on what day or at what time water will be delivered to them.
Why do people need to be home when the water is on? Can they have a storage container that fills automatically when water is delivered?
This is exactly what some households do, if they have an underground tanks or tanks on their roof. However, most middle- and low-income households cannot afford the expense of installing underground tanks, and many houses are not strong enough to support the weight of large tanks full of heavy water on their roof. While a small tank that automatically fills inside or just outside of a house at ground level may be possible if you only need to store 200-300 liters, households often need to store much more water than that to meet their families' needs between supply cycles. Since they do not have the money or space for huge storage containers, they fill every small container they can and store them around the house. They may wash dishes and clean laundry while the water is on so that they do not need to store as much water. Also, it is common for the tap to be located outside the home or for several households to collect water from the same tap, so people need to be present when the water is on to carry it home bucket by bucket.
There are many reasons that distribution systems provided intermittent water supply: with the current state of the distribution system, if water were to be suddenly turned on to all areas at once, not all people would be able to get enough water. One author has suggested that three types of scarcity can lead to or perpetuate intermittent water supply: poor management, economic scarcity, and absolute scarcity (Totsuka et al, 2004). For example, electricity to run pumps that take water from a lake or river may be interrupted frequently, which would interrupt flow of water. The water treatment plant or pipes may not be big enough to process the amount of water needed for everyone at once. Pipes with too many leaks could cause millions of liters of water to be lost to the ground if the pipes were always kept under pressure. Sometimes so many repairs need to be made that a utility turns off the supply every day to make the repairs. In some cases, there might not be enough water at the source.
Some are; there are a few pilot projects of continuous supply, known as 24x7, in Karnataka and Maharashtra. Other cities in Asia, such Phnom Penh in Cambodia and Manila in the Philippines, have switched from intermittent to continuous supply (Seetharam and Bridges, 2005). In order to accomplish this, usually the pipes must be repaired to reduce leakages and meters installed to control water loss and water demand (World Bank, 2003). Repairing and increasing the capacity of water distribution system infrastructure to switch to continuous supply is very expensive and likely out of reach for many utilities in the short term. The 24x7 pilot projects in India have been years in the planning and still just begun. While continuous supply is the long-term vision for most utilities, intermittent supply is the reality of water access for millions of people around the world that has been in existence for decades and will continue to be for many more. Some researchers suggest that increasing scarcity of water from climate change and increasing demand may in fact make in fact make intermittent supply more common (Vairavamoorthy et al, 2008).
van den Berg, C. and Danilenko, A. (2011) The IBNET Water Supply and Sanitation Performance Blue Book: The International Benchmarking Network for Water and Sanitation Utilities Databook, Washington, DC, World Bank. http://www-wds.worldbank.org/external/default/WDSContentServer/WDSP/IB/2011/01/07/000334955_20110107044636/Rendered/PDF/588490PU
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Vairavamoorthy, K., Gorantiwar, S. D., and Pathirana, A. (2008) Managing urban water supplies in developing countries - Climate change and water scarcity scenarios. Physics and Chemistry of the Earth, 33(5), 330–339.
WHO and UNICEF (2000) “Annex A Methodology for the Global Water Supply and Sanitation Assessment 2000” in Global Water Supply and Sanitation Assessment 2000 Report. Geneva, WHO/UNICEF, 77–79. http://www.who.int/water_sanitation_health/monitoring/jmp2000.pdf
World Bank (2003) Nagari: 24-hour Water Supply: Is this Goal Achievable?, Hyderabad, India, World Bank Water and Sanitation Program. http://www.waterlinks.org/sites/default/files/24-Hour%20Water%20Supply.pdf