Water distribution

Out of all the water on only 2.75 percent is fresh water, including 2.05 percent frozen in 0.68 percent as and 0.0101 percent of it as in lakes and rivers. Freshwater lakes, most notably in Russia and the in North America, contain seven-eighths of this fresh surface water. Swamps have most of the balance with only a small amount in rivers, most notably the The atmosphere contains 0.04% water. In areas with no fresh water on the ground surface, fresh water derived from precipitation may, because of its lower density, overlie saline ground water in lenses or layers.

Water is a critical issue for the survival of all living organisms. Some can use salt water but many organisms including the great majority of higher plants and most must have access to fresh water to live. Some terrestrial mammals, especially desert appear to survive without drinking but they do generate water through the of seeds and they also have mechanisms to conserve water to the maximum degree.