<P> Water is also used in many large scale industrial processes, such as thermoelectric power production, oil refining, fertilizer production and other chemical plant use, and natural gas extraction from shale rock . Discharge of untreated water from industrial uses is pollution . Pollution includes discharged solutes (chemical pollution) and increased water temperature (thermal pollution). Industry requires pure water for many applications and utilizes a variety of purification techniques both in water supply and discharge . Most of this pure water is generated on site, either from natural freshwater or from municipal grey water . Industrial consumption of water is generally much lower than withdrawal, due to laws requiring industrial grey water to be treated and returned to the environment . Thermoelectric powerplants using cooling towers have high consumption, nearly equal to their withdrawal, as most of the withdrawn water is evaporated as part of the cooling process . The withdrawal, however, is lower than in once - through cooling systems . </P> <P> It is estimated that 8% of worldwide water use is for domestic purposes . These include drinking water, bathing, cooking, toilet flushing, cleaning, laundry and gardening . Basic domestic water requirements have been estimated by Peter Gleick at around 50 liters per person per day, excluding water for gardens . Drinking water is water that is of sufficiently high quality so that it can be consumed or used without risk of immediate or long term harm . Such water is commonly called potable water . In most developed countries, the water supplied to domestic, commerce and industry is all of drinking water standard even though only a very small proportion is actually consumed or used in food preparation . </P> <P> Sustainable management of water resources (including provision of safe and reliable supplies for drinking water and irrigation, adequate sanitation, protection of aquatic ecosystems, and flood protection) poses enormous challenges in many parts of the world . </P> <P> Recreational water use is usually a very small but growing percentage of total water use . Recreational water use is mostly tied to reservoirs . If a reservoir is kept fuller than it would otherwise be for recreation, then the water retained could be categorized as recreational usage . Release of water from a few reservoirs is also timed to enhance whitewater boating, which also could be considered a recreational usage . Other examples are anglers, water skiers, nature enthusiasts and swimmers . </P>

What are the various water resources on earth