<P> Water allocation between competing users is increasingly determined by application of market - based pricing for either water licenses or actual water . </P> <P> Water, in absolute terms, is not in short supply planet - wide . But, according to the United Nations water organization, UN-Water, the total usable freshwater supply for ecosystems and humans is only about 200,000 km3 of water--less than one percent (<1%) of all freshwater resources . Usable fresh water includes water not contaminated or degraded by water - altering chemicals, such as sewage or any other harmful chemicals from continuous previous use . And, water use has been growing at more than twice the rate of the population increase in the last century . Specifically, water withdrawals are predicted to increase by 50 percent by 2025 in developing countries, and 18 per cent in developed countries . One continent, for example, Africa, has been predicted to have 75 to 250 million lacking access to fresh water . By 2025, 1.8 billion people will be living in countries or regions with absolute water scarcity, and two - thirds of the world population could be under stress conditions . </P> <P> The most common threat to water security is water scarcity . There can be several causes to water scarcity including low rainfall, climate change, high population density, and overallocation of a water source . An example of periodic water scarcity in the United States is droughts in California . Another category of threats to water security is environmental threats . These include contaminates such as biohazards (biological substances that can harm humans), climate change and natural disasters . Contaminants can enter a water source naturally through flooding . Contaminants can also be a problem if a population switches their water supply from surface water to groundwater . Natural disasters such as hurricanes, earthquakes, and wildfires can damage man - made structures such as dams and fill waterways with debris . Other threats to water security include terrorism and radiation due to a nuclear accident . </P> <P> According to Nature (2010), about 80% of the world's population (5.6 billion in 2011) live in areas with threats to water security . The water security is a shared threat to human and nature and it is pandemic . Human water - management strategies can be detrimental to wildlife, such as migrating fish . Regions with intensive agriculture and dense populations, such as the US and Europe, have a high threat of water security . Water is increasingly being used as a weapon in conflict . Water insecurity is always accompanied by one or more issues such as poverty, war and conflict, low women's development and environmental degradation . Researchers estimate that during 2010 - 2015, ca US $800 billion will be required to cover the annual global investment in water infrastructure . Good management of water resources can jointly manage biodiversity protection and human water security . Preserving flood plains rather than constructing flood - control reservoirs would provide a cost - effective way to control floods while protecting the biodiversity of wildlife that occupies such areas . </P>

Three reasons responsible for water scarcity in india