Environmental Science (2+1)

Water distribution

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


• Only three percent of the water on Earth is freshwater, and about two-thirds of this is frozen in glaciers and most of the rest is underground and only 0.3 percent is surface water. Freshwater lakes, most notably Lake Baikal in Russia and the Great Lakes 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 Amazon River. The atmosphere contains 0.04% water. In areas with no freshwater on the ground surface, freshwater derived from precipitation may, because of its lower density, overlie saline ground water in lenses or layers.
• Aquatic organisms
• Agriculture
• Limiting resource
• Freshwater withdrawal
• Causes of limited fresh water
• Another source of fresh water