The water covers 70% of the land but only a small amount is available for humans, is the 60/80% of the weight of living organisms. Water is also used by plants (photosynthesis) and industries. Industries, in fact, 30% of the total water use. The composition is liquid water, ice and steam. The main cause of water pollution is the waste of water, in fact, a problem, according to environmentalistsis 'water shortage'. Environmentalists say that, within 25 years, freshwater for drinking and not sufficient for irrigation. The industry waste and the organic waste are other causes of pollution of water.
A solution of 'water shotage' is desalination. It is a process which transforms sea water into potable water. But I think that this solution isn't economic. Infact I think that we should to reduce waste domestic water, we should to install the wells of rainwater in the gardens.
The water cycle starts because solar energy heats water on the surface, and cause an important phenomenon, that is called evaporation. After, water vapour condenses in clouds and falls back onto the surface as precipitation and other weather . Finally, the water is evaporate and begin the cycle over again.
There are important processes that make up the water cycle, that are called evaporation, condensation, runoff, evapotranspiration and precipitation. Precipitation is very important for plant and soil.
Groundwater is an important part of the water cycle because the part of precipitation that seeps down through the soil until it reaches rock material.