Freshwater is an important renewable resource, necessary for the survival of most terrestrial organisms, and is required by humans for drinking and agriculture, among many other uses. The UN estimates that about 1.2 billion people (18 percent of the world's population) lack access to safe drinking water.1

Numerical definition

Freshwater is defined as water with less than 0.5 parts per thousand dissolved salts. Freshwater bodies include lakes and ponds, rivers, some bodies of underground water and many kinds of man-made freshwater bodies, such as canals, ditches and reservoirs. The ultimate source of freshwater is the precipitation of atmosphere in the form of rain and snow.

Water distribution

Access to unpolluted freshwater is a critical issue for the survival of many species, including humans, who must drink freshwater in order to survive. Only three percent of the water on Earth is freshwater in nature, and about two-thirds of this is frozen in glaciers and polar ice caps. 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

Freshwater creates a hypotonic environment for aquatic organisms. This is problematic for some organisms, whose cell membranes will burst if excess water is not excreted. Some protists accomplish this using contractile vacuoles, while freshwater fish excrete excess water via the kidney. Although most aquatic organisms have a limited ability to regulate their osmotic balance and therefore can only live within a narrow range of salinity, diadromous fish have the ability to migrate between freshwater and saline water bodies. During these migrations they undergo changes to adapt to the surroundings of the changed salinities; these processes are hormonally controlled. The eel (Anguilla anguilla) uses the hormone prolactinFact: date=September 2008, while in salmon (Salmo salar) the hormone cortisol plays a key role during this process.Fact: date=September 2008

Nature Activity VS Human Activity

Agriculture- Change of Landscape

Changing landscape for the use of agriculture creates a great effect on flow of freshwater and surrounding. Reshaping a large scale of landscape in creating lands that are suitable for agriculture changed the flow and sustainability of freshwater which result in effecting the sustainability of the local ecosystem. Changes in landscape through the remove of trees and soils changed the local environments flow of freshwater and also effect the cycle of freshwater. As a result more freshwater are consumed and stored in soil which benefits agriculture. However, since “agriculture was the human activity that consumes the most freshwater” (Gordon L., D. M. ,2003, P.1973-1984), freshwater would be used up completely which result in scarcity and destroy of local ecosystem. Similar to events happening in Australia where too much land and freshwater flow are restructured for the use of agriculture, which ends up causing “33% of lands area at risk of salinization and scarcity” (Gordon L., D. M. ,2003, P.1973-1984). Redesigning lands for the maximum use of agriculture will certainly bring a great damage to the environment and reduces the available freshwater supply since freshwater is a limiting natural resource.