Freshwater Resources: Past, Present, Future

Freshwater is a crucial resource for human life and natural systems. It is defined as water containing less than 500 ppm of dissolved salts and constitutes only 2.5% of the total water on earth. Most is stored in ice caps, soil moisture, and groundwater reservoirs, and only a small percentage is accessible for sustainable uses (in lakes, rivers, shallow reservoirs). Freshwater availability changed during human history as a result of increasing drainage and diversions for agriculture as well as impounds and other constructions for hydropower use and flood control. Despite its apparent scarcity, it is of fundamental importance for every form of life and its availability is threatened by climate change and other human pressures. It is now recognized that measures to globally protect freshwater ecosystems and the services they provide are needed. However, competition exists between human and environmental needs, which form part of an ongoing debate.