Surface freshwater resources include streams, rivers, lakes and wetlands. This makes up less than 0.3 percent of the total water supply. The main source of surface water is rainfall, but much is lost to evaporation. Surface freshwater is usually drawn direct from lakes or man-made reservoirs.
Groundwater, which is found in soil and rock beneath the water table, is an important source of freshwater. Groundwater supplies around 95 percent of all drinking water in the United States. Municipal authorities draw freshwater from underground sources, treating it to remove impurities.
The polar icecaps and glaciers of Antarctica and Greenland account for 70 percent of the Earth's natural freshwater resources. This huge freshwater resource is largely unavailable for human use, because of its inaccessibility. Melting polar ice quickly becomes saline as it mixes with salty ocean water.
Salty ocean water makes up more than 95 percent of all water on Earth. Desalination is an industrial process that removes salt from ocean water so that it can be used for drinking, agriculture and industry. Desalination is increasingly popular in arid parts of the world with scarce natural freshwater resources. The process is costly and requires large amounts of power. New desalination plants often use renewable energy sources, such as solar or wind power, to reduce costs.
