Almost all waters of the hydrosphere of any territory (region), country or globe are suitable for use: rivers, lakes, seas and oceans, groundwater, soil moisture, glacier water, atmospheric water vapor, and water of man-made structures - reservoirs and canals. 

The total volume (non-recurrent supply) of water resources is 1390 million km³, of which about 1340 million km³ is water of the World Ocean. Less than 3% is freshwater, of which only 0.3% is technically available for use. 

Water resources are considered renewable, although it is not yet clear how fast water resources are renewed after use and how much their scarcity threatens the Earth's ecosystem. Technologies also exist for desalination of saline seawater. 

The countries with the largest reserves of fresh water in the world are Russia, Canada and Brazil. Every year, on 22 March, the United Nations celebrates World Water Day. About 98% of all the fresh water in the Earth's liquid state is in the groundwater, but only about 50% of it is found at depths of 800 m or less. Only 0.01% of all freshwater in the liquid state is found in rivers and streams and 1.47% in lakes.