Water glossary

Access to safe water Measured by the number of people who have a reasonable means of getting an adequate amount of clean water, expressed as a percentage of the total population. In urban areas 'reasonable' access means there is a public fountain or water spigot located within 200 metres of the household. In rural areas, it implies that members of the household do not have to spend excessive time each day fetching water. Water is safe or unsafe depending on the amount of bacteria in it. An adequate amount of water is enough to satisfy metabolic, hygienic, and domestic requirements, is about 25-50 litres per person per day.   Access to sanitation Refers to the share of the population with at least adequate excreta disposal facilities, effectively preventing human, animal, and insect contact with excreta. Suitable facilities range from simple but protected pit latrines, to flush toilets with sewerage. To be effective, all facilities must be correctly constructed and maintained. Sanitation is an important public health measure which is essential for the prevention of disease.   Aquifer  A layer of sand or porous rock that holds water lying between layers of non-porous rock.   Distillation The process of boiling water, collecting the steam (or water vapour) and turning the steam back into liquid again.   Filtration  The process of passing water through a porous substance to remove solids in suspension.   Groundwater  A layer of underwater water, flowing within an aquifer . It may come to the surface at springs or seepage to form oases or swamps. Humans may draw this water from wells or bores for agricultural, household and industrial use. It is replenished through surface seepage but this may take many years depending on the depth of the aquifer. The rate of withdrawal commonly exceed the rate of recharge, and in many areas the groundwater supply is declining.   Irrigation The provision of water for crops. The water may be obtained from surface storage, such as lakes or dams, or from groundwater.   Malaria A life-threatening parasitic disease transmitted by mosquitoes and characterised by high fever. It causes 350-500 million infections and approximately 1.3 million deaths annually, mainly in the tropics.   Oral Rehydration Therapy (ORT) An inexpensive glucose (sugar) and electrolyte (salt) solution which has substantially reduced the number of deaths from dehydration due to diarrhoea.   Surface water Water on the ground or in a stream, river, lake, sea or ocean; as opposed to groundwater.   Virtual water The water used to produce the goods that a country imports. It is the water that a country would otherwise require to produce the goods it is imports.   Water governance The political, economic, administrative, social processes and institutions by which public authorities, communities and the private sector take decisions on how best to develop and manage water resources.   Water footprint The volume of water needed for the production of goods and services consumed by the inhabitants of a country.   Water scarcity When annual water supplies drop below 1,000 cubic metres per person.   Water stress When annual water supplies drop below 1,700 cubic metres per person.   Water-based diseases Diseases caused by parasites which spend part of their life cycle in organisms living in water, for example drancunculiasis (guinea worm) and schistosomiasis (bilharzia).   Water-borne diseases Diseases caused by drinking contaminated water, for example diarrhoea, cholera, typhoid, poliomyelitis and hepatitis A. Sudden outbreaks of water-borne diseases can occur when natural disasters damage water supply.   Water-related diseases Diseases caused by insects that feed or breed in water, for example malaria and onchocerciasis (river blindness).   Water-washed diseases Diseases caused by poor personal hygiene or washing with contaminated water, for example scabies and trachoma.