Distribution of Water
Water is the substance that makes possible for earth to support life. Water is present in three forms: solid (ice), liquid (water) and gaseous state (water vapour). Water is the most common substance on the earth – almost three times as common as every other substance (beside water) combined. 97% is seawater, 2% is locked in ice caps and glaciers, and 1% lies too far underground to retrieve. Only 1/3% is fresh water that can be used for drinking; of this 3/4th is locked up in the Antartic ice cap. Without the minute percentage of water that is available to us for drinking, we can not survive for more than a few days at the most, for 65% of body consists of water.
 The Beginning
Water on the earth is always in movement and is always changing states, from liquid to vapour to ice and back again. The water cycle has been working for billions of years and all life on earth depends on it continuing to work. In the beginning of earth’s life earth was an incandescent sphere made of hot magma. Water is a component of all magmas. As the earth cooled down, and water was set free by the magma, water could stay on the surface as a liquid. Meanwhile volcanic activity kept introducing water in the atmosphere, thus increasing the surface- and ground-water volume of the earth. This process of volcanic activity still continues.
 The Cycle
The water cycle is truly a circular process and there is no beginning or end of this process. But, since most of earth’s water exists in the oceans, that is where we will begin. The sun, because of the heat that it transfers to the earth drives the water cycle. Sun’s energy heats up water in the oceans. A small proportion of the water evaporates and takes the form of vapour in the air in the atmosphere. Some evaporation also takes place from the water on the land. In addition plants, in a process called transpiration, release water into the air. The water vapour rises into the air where cooler temperatures cause it to condense into clouds. These clouds are moved around the globe by the air currents. Meanwhile clouds grow and collide with each other and fall on the surface of the earth as precipitation.
The precipitation takes many forms depending on the temperature, for example dew, rain, hail and snow. Rain and snow are the main forms of precipitation. Some precipitation falls as snow and accumulates as ice caps and glaciers, which can store frozen water for thousands of years. The other part of snow melts over a few weeks, and the melted water flows down. However, most precipitation falls back into the oceans or onto land, where, due to gravity, the precipitation flows over the ground as surface runoff, a portion of it ending up in oceans. Another portion added to groundwater – some water infiltrates deep into the ground and replenishes aquifers (saturated subsurface rock), which store huge amounts of freshwater for long periods of time. Some groundwater stays close to the land surface and can seep back into surface-water bodies (and the ocean) as ground-water discharge, and some ground water finds openings in the land surface and emerges as freshwater springs. Some water is stored as freshwater in lakes. Most water ends up back in the oceans.
This cycle then repeats itself over and over again. At any given time just .005 percent of the worlds total water supply is moving through the hydrologic cycle.
 Components of the water cycle
Fifteen components of the water cycle are identified:
- Water storage in oceans
- Water in the atmosphere
- Water storage in ice and snow
- Snowmelt runoff to streams
- Surface runoff
- Freshwater storage
- Ground-water storage
- Ground-water discharge
 Dangers to The Water Cycle
Water Cycle is endangered by water pollution. Water pollution occurs from
- Chemical pollution, a result of the absence of or inefficient operation of industrial wastewater treatment plants. This in turn affects the surface waters or groundwater.
- Organic human and animal waste discharged into the river gives birth to viruses and pathogenic bacteria. Though, organic waste has the ability to purify naturally, but if it arrives faster and in large quantities, it leads to microbiological contamination.
- The concentration of stockbreeding, chemical fertilisers (nitrates and phosphates), herbicides, insecticides and other agrochemical products in agricultural lands also disturbs the water cycle.
- The black water (sinks and toilets) and grey water (washing machines, showers, etc) released by households.
 Impact of disturbing the Water Cycle
Nature has its own way of restoring the imbalance caused by organic waste. Through natural purification, a process where a living environment can transform and naturally eliminate (fully or partially) the pollutant affecting it, the balance of the ecosystem is preserved. However, this is not possible when pollution increases at a rate which far exceeds the rate at which natural purification is taking place. This results in poisonous drinking water, unbalanced river and lake ecosystems that can no longer support full biological diversity and deforestation from acid rain. It also has an adverse impact on the food cycle. Little microscopic animals called zooplankton eat the affected algae, and are in turn eaten by the fish. The fish produce body wastes and they eventually die. Moreover, when the fish eats plants which have chemicals, it ends up getting sick and dies.
It is important to initiate a worldwide effort to monitor and restrict global pollution as most forms of pollution do not respect national boundaries.
- The Water Cycle
- Life and Biogeochemical Cycles
- Biogeochemical Cycles