Water : About two thirds of the Earth is covered with water.
The water in the oceans and seas has many salts dissolved in it — the water is saline. So, it is not fit for drinking and other domestic, agricultural and industrial needs.
Note:- “Rime of the Ancient Mariner” written by S.T. Coleridge in 1798.
The water vapour in the air condenses to form tiny droplets of water, which appear as clouds. Many tiny water droplets come together and fall down as rain, snow or hail.
Water cycle:-
Water from the ocean and surface of the earth goes into air as vapour; returns as rain, hail or snow and finally goes back to the oceans.
The circulation of water in this manner is known as the water cycle. This circulation of water between ocean and land is a continuous process. This maintains the supply of water on land.
A part of the rainwater gets absorbed by the ground and seems to disappear in the soil. Some of this water is brought back to the air by the process of evaporation and transpiration. The rest seeps into the ground. Most of this water becomes available to us as ground water.
The time, duration and the amount of rainfall varies from place to place. In some parts of the world it rains throughout the year while there are places where it rains only for a few days.
In our country, most of the rainfall occurs during the monsoon season. Rains bring relief especially after hot summer days. The sowing of many crops depends on the arrival of monsoon.
Excess of rainfall may lead to many problems. Heavy rains may lead to rise in the level of water in rivers, lakes and ponds. The water may then spread over large areas causing floods.
In our country, floods cause extensive damage to crops, domestic animals, property and human life.
What happens if it does not rain for a long time:-
- The soil continues to lose water by evaporation and transpiration. Since it is not being brought back by rain, the soil becomes dry.
- The level of water in ponds and wells of the region goes down and some of them may even dry up.
- The ground water may also become scarce. This may lead to drought.
Rain water Harvesting :- One way of increasing the availability of water is to collect rainwater and store it for later use. Collecting rainwater in this way is called rainwater harvesting. The basic idea behind rainwater harvesting is “Catch water where it falls”.
Techniques of rain water Harvesting :-
- Rooftop rainwater harvesting: In this system the rainwater is collected from the rooftop to a storage tank, through pipes. This water may contain soil from the roof and need filtering before it is used.
- allow water to go into the ground directly from the roadside drains that collect rainwater