Water is essential for life. About two thirds of the Earth is covered with water. Most of this water is in ocean and sea. 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. Yet, oceans play an important role in supplying the water that we use. After all, the water that we use is not salty. Many of us live in places far away from the oceans.
Does the water supply in these places also depend on the oceans? How does the ocean water reach ponds, lakes, rivers and wells, which supply us water? How come the water from these sources is not saline anymore? That is where the water cycle comes in!
Does the water supply in these places also depend on the oceans? How does the ocean water reach ponds, lakes, rivers and wells, which supply us water? How come the water from these sources is not saline anymore? That is where the water cycle comes in!
Interesting facts: About two glasses of water are required to produce each page of a book.
WATER CYCLE
Disappearing Trick of Water
During the daytime, sunlight falls on the water in oceans, rivers, lakes and ponds. The fields and other land areas also receive sunlight. As a result, water from all these places continuously changes into vapour. However, the salts dissolved in the water are left behind during the daytime all the air surrounding us gets heated.
This warm air provides heat for evaporation of water in the shade. Thus, evaporation takes place from all open surfaces of water. As a result, water vapour gets continuously added to air.
However, evaporation of water is a slow process. That is why we rarely notice its loss from a bucket full of water.
LOSS OF WATER BY PLANTS
Remaining part of this water is released by the plants into air, as water vapour through the process of transpiration. Water vapour enters the air through the processes of evaporation and transpiration.
Notes:-wheat plants that give us one kilogram of wheats require nearly 500 litres water, that is, roughly 25 large sized buckets full of water.
HOW ARE CLOUDS FORMED?
The process of condensation plays an important role in bringing water back to the surface of earth. As we go higher from the surface of the earth, it gets cooler. When the air moves up, it gets cooler and cooler.
At sufficient heights, the air becomes so cool that the water vapour present in it condenses to form tiny drops of water called droplets. It is these tiny droplets that remain floating in air and appear to us as clouds. It so happens that many droplets of water come together to form larger sized drops of water.
Some drops of water become so heavy that they begin to fall. These falling water-drops are, what we call rain. In special conditions, it may also fall as hail or snow. Thus, water in the form of vapour goes into air by evaporation and transpiration, forms clouds, and then comes back to the ground as rain, hail or snow.
BACK TO THE OCEANS
Almost all land surfaces are above the level of oceans. Most of the water that falls on the land as rain and snow sooner or later goes back to the oceans. This happens in many ways. Snow in the mountains melts into water. This water flows down the mountains in the form of streams and, rivers. Some of the water that falls on land as rain, also flows in the form of rivers and streams. Most of the rivers cover long distances on land and ultimately fall into a sea or an ocean. However, water of some rivers flows into lakes.
The rainwater also fills up the lakes and ponds. 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. Open wells are fed by ground water. Ground water is the source for many lakes as well. It is also this ground water which is drawn by a handpump or a tubewell. The more handpumps or tubewells that are used in an area, the deeper we need to dig to find this ground water. The loss in the level of ground water due to over use, is worrisome.
In those areas where the land has little or no vegetation, the rainwater flows away quickly. Flowing rainwater also takes the top layer of the soil away with it. There are few areas where most of the land is covered with concrete. This reduces the seepage of rainwater into the ground which ultimately affects the availability of ground water.
We now know that water brought back to the surface of the earth by rain, hail or snow, goes back to oceans. Thus, 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.
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WHAT IF IT RAINS HEAVILY?
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 hotsummer days. The sowing of many crops depends on the arrival of monsoon. However, 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. The crop fields, forests, villages, and cities may get submerged by water. In our country, floods cause extensive damage to crops, domestic animals, property and human life.
During floods, the animals living in the water also get carried away with the waters. They often get trapped on land areas and die when floodwater recedes. Rains also affect the animals living in the soil.
WHAT HAPPENS IF IT DOES NOT RAIN FOR A LONG PERIOD?
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. In drought conditions, it is difficult to get food and fodder.
HOW CAN WE CONSERVE WATER?
Only a small fraction of water available on the Earth is fit for use of plants, animals and humans. Most of the water is in the oceans and it cannot be used directly. When the level of the ground water decreases drastically, this can not be used any more. The total amount of water on Earth remains the same, but, the water available for use is very limited and is decreasing with over usage.
The demand for water is increasing day-by-day. The number of people using water is increasing with rising population. more and more water is being used for producing food and by the industries. These factors are leading to shortage of water in many parts of the world.
RAINWATER 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”.
Here are two techniques of rainwater harvesting:
1. 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. Instead of collecting rainwater in the tank, the pipes can go directly into a pit in the ground. This then seeps into the soil to recharge or refill the ground water.
2. Another option is to allow water to go into the ground directly from the roadside drains that collect rainwater.
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