When we think of water, we think of rivers, sea, waterfall, rains, etc. Rain puddles are formed in the rainy season. By noon, the puddles vanish. The puddles disappear because the sun's heat causes evaporation that changes water into water vapour. Water vapour cools to form clouds and from clouds we get rain, snow or sleet.
Water Cycle
The process by which water continually changes its form and circulates between oceans, atmosphere and land is called the water cycle.
Fig: Water Cycle
Our earth is like a terrarium. The same water that existed centuries ago still exists today.
Sources of Water
Water sources can be broadly classified into:
- Fresh water sources: These include the rivers, ponds, springs and glaciers.
- Saline water source: Ocean bodies and seas form a part of this. The water of the ocean is saline because it contains huge amounts of dissolved salts. Most of this salt is sodium chloride commonly known as the common table salt that we eat daily.
Distribution of Water
Fig: Water on Earth
Three–fourths of the earth's surface is covered by water. But most of this water is available as saline water in oceans and seas. Freshwater is a small fraction of total water on earth. Due to this, in spite of living on the Blue Planet, we face shortage of drinking water. The following table shows the distribution of water in percentage.
| Water Body | Percentage |
|---|---|
| Ocean | 97.3 |
| Ice-caps | 2.0 |
| Groundwater | 0.68 |
| Freshwater Lakes | 0.009 |
| Inland Sea and Salt Lakes | 0.009 |
| Atmosphere | 0.0019 |
| Rivers | 0.0001 |
| Total | 100 |
Conservation of Water
Since water is very important for us and scarce too, we must take measures for conservation of this precious resource. Some of the steps to prevent wastage of water are as under:
- Close taps when not in use
- Repair all tap leakages immediately
- Do rainwater harvesting
- Use water filled in the bucket for bathing instead of a bath tub/shower.