Drinking water or potable water is water that is safe for ingestion, either when drunk directly in liquid form or consumed indirectly through food preparation. It is often supplied through taps, in which case it is also called tap water.
The amount of drinking water required to maintain good health varies, and depends on physical activity, age, health-related issues, and environmental conditions. For those who work in a hot climate, up to 16 liters (4.2 U.S. gal) a day may be required.
Water storage is a broad term referring to storage of both potable water for consumption, and non potable water for use in agriculture. In both developing countries and some developed countries found in tropical climates, there is a need to store potable drinking water during the dry season. In agriculture water storage, water is stored for later use in natural water sources, such as groundwater aquifers, soil water, natural wetlands, and small artificial ponds, tanks and reservoirs behind major dams. Storing water invites a host of potential issues regardless of that water's intended purpose, including contamination through organic and inorganic means.
Slow sand filters are used in water purification for treating raw water to produce a potable product. They are typically 1–2 m (3.3–6.6 ft) deep, can be rectangular or cylindrical in cross section and are used primarily to treat surface water. The length and breadth of the tanks are determined by the flow rate desired for the filters, which typically have a loading rate of 200–400 litres (0.20–0.40 m) per square metre per hour.
Slow sand filters differ from all other filters used to treat drinking water in that they work by using a complex biofilm that grows naturally on the surface of the sand. The sand itself does not perform any filtration function but simply acts as a substrate, unlike its counterparts for ultraviolet and pressurized treatments. Although they are often preferred technology in many developing countries because of their low energy requirements and robust performance, they are also used to treat water in some developed countries, such as the UK, where they are used to treat water supplied to London. Slow sand filters now are also being tested for pathogen control of nutrient solutions in hydroponic systems.
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