Gain et al.  define a Global Water Security Index  metric on a scale of 0 to 1 combining indicators of relative levels of availability of freshwater, accessibility to water services, water management and water quality and safety . Global application of this index indicates large worldwide differences in water security arising from different combinations of reasons . In North Africa, the Middle East, large parts of the Indian sub-continent and north China, low water security arises predominantly from low water availability. However, many areas with relatively high water availability have relatively low levels of water security due to other factors. In 2015, 29% of the world's population did not have access to safe drinking water . In large parts of South and Southeast Asia, significant contributions to water insecurity came from increased flood risk and deteriorated water quality . Water availability is relatively high across most of Africa, but water security is relatively low due to low accessibility, management and safety/quality standards. Most people in Africa do not have access to safe drinking water and improved sanitation .
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