We all depend on the same vital substance water, diverse by its nature, it is solid, vapour and liquid. It is in the air, on the earth
surface and within the ground ever-changing and giving shape to a dramatic range of natural ecosystems. For the earth's
inhabitants, diversity of the resource also means great disparities in well being and development . As we degrade the quality
of our water and modify the natural ecosystems on which people and life depend, we also threaten our own survival. 


Water is the most widely occurring substance on this planet. Globally distributed by the hydrological cycle, or driven by the energy
cycle, the circulation of water powers most of the other natural cycles and conditions the weather and climate. Water has shaped
the earth's evolution and continues to fashion Its programmes. This is the water precipitated from the atmosphere on to land,
where it may be stored in liquid or solid form, and can move laterally and vertically and between one phase and another phase
by evaporation, condensation , freezing and thawing on the land surface. We are aware that about 71 % of the earth's surface
Is covered with water. Almost all the water on the earth is contained in the seas and oceans, rivers , lakes, ice caps, as
groundwater and in the atmosphere. However, most of this water is not fit for human consumption. 
1. Pure water is a colourless, odourless, tasteless, transparent liquid. 
2. Water exists in all he three states, solid (as ice), liquid (as water) and gas (as water vapour). 


When water circulates through the water cycle it can be found in all the three forms i.e., solid , liquid and gas -at any given
time somewhere on the earth. The solid form, snow and ice, is present as ice caps at the poles of the earth, snow covered
mountains and glaciers. Liquid water is present in oceans, lakes, rivers and even underground. The gaseous form is the
water vapour present in the air around us. The continuous cycling of water among its three forms keeps the total amount
of water on the earth constant. 


The supply of water in nature does not run out. This is because water is continuously recycled in the water cycle. 
1. Heat from the sun causes the water on the earth's surface to evaporate. The vapour rises, cools and condenses to
form tiny water droplets. These droplets form clouds. 
2. The clouds get carried along by air currents. They cool and the droplets join to form larger drops. These fall as mist. 
3. If the temperature in the region is very low, these water droplets fall as hail, sleet or snow. 
4. Some of the rain water flows along the ground as streams. Some soaks through the ground and then reappears
as springs. Streams and springs join to form rivers. Rivers flow back into the sea. Thus the water cycle is complete. 


Ground water is an important source of water. If we dig a hole in the ground near a water body we may find that the