THE water-drops that fall from the sky in the form of rain, hail, or snow have been a part of the water cycle since Earth’s birth. Water moves or transforms from one form to another at different stages. The heat of the sun is a constant source of energy that makes the journey of water or water cycle possible.

We all know that water passes through three different phases — liquid in the form it is found in ocean, river, lakes, ponds and underground; solid in the form of ice; and gas in the form of vapour through the processes of evaporation, condensation, precipitation, infiltration, runoff and subsurface flow.

Here we shall look at the important states and sources of water.

Glaciers

At high altitude water exists in the form of snow or ice and accumulates on high mountains, thus forming glaciers where most of the freshwater is trapped. The snow stays in large amount and is a constant source of water for rivers and lakes in summer. The ice sheets which are a form of glaciers are mostly found in Greenland and Antarctica. The Polar regions constitute 99 per cent of glacial ice. The main sources of glaciers are the Himalaya and Andes.

Rivers

Besides rainfall, the snow mass or glaciers when flow down to the lowland areas form streams and rivers. Water moves to the rivers through runoff or small streams. Rivers ultimately fall into the huge water body called ocean.

Rivers are formed in different sizes and shapes which move water from upland to lowland. Rivers are important sources of food and agriculture for millions of people around the world. River Nile in Africa is the longest river of the world. As the surface of water is exposed to the sunlight it evaporates back to the atmosphere. River Indus which is the longest river in Pakistan is fed with glaciers.

Lakes

Lakes are water bodies where large amount of water gets stored. Mostly lakes are formed in a depression in the land where water accumulates through melting snow or rainfall.

Lakes hold water like gigantic water tubs. Lakes are usually full of freshwater. Depending upon the surface area of lakes, water evaporation will take place to become part of the atmosphere. Ponds and reservoirs also contribute to water storage.

Groundwater

It is the water that is not usually seen. It is also a source of springs, rivers and streams. The groundwater is also taken up by plants for their growth and minerals intake.

Aquifier and water table are some of the terms used for groundwater.

Oceans

About 70 per cent of the Earth’s surface is covered with oceans which contain almost 97 per cent of the Earth’s water. The oceans affect the weather and temperature. The role of oceans in rain and snow formation is immense. The salty water of the oceans is also a source of salt. The four famous oceans on Earth which are connected are the Arctic, Atlantic, Indian and the Pacific.

Atmosphere

Not only there is water on the land but atmosphere is also a source of potential water. Mostly humidity indicates the moisture contents in the air. Evaporation and transpiration are the main processes of the atmospheric water.

The sun helps to evaporate the water and it accumulates and condenses in the atmosphere which form clouds and result in precipitation. In this way the water comes back to the earth and so the story goes on.