CLASS 7-Water: A Precious Resource-Chapter Note

CBSE CLASS 7-Water: A Precious Resource-Chapter Note

Why is water persious?

The total amount of
(i) water in the rivers andlakes of the world remains constant.
(ii) water under the ground remains constant.
(iii) water in the oceans and seas of the world remains constant.
(iv) water of the world remains constant.

Resources of water on earth

The three main sources of water are:

• Rainwater.
• Groundwater means water bodies like Wells and Springs.
• Surface water means different water bodies like Sea, Oceans, Reservoirs, Rivers, Streams, Ponds, Lakes and Tanks.

Water available on earth

Our planet is known as blue planet by there is very less amout of water on earth to drink

Forms of water

• water on the earth is maintained form millions of years by various processes which make the water cycle.
• The solid form of water ice and snow, 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 ungerground.
• The gaseous form of water is the vapour present in the air around us.
• The continuous cycle of water among its three states keeps the total amount of water on the earth constant even when the whole world is using it.

Ground Water is an source of water

• Ground near a water body observed that the soil is moist.
• The moisture in the soil shows the presence of water underground.
• If we dig deeper into the soil we would reach a level where all the space between particles of soil and gaps between rocks are filled with water.
• The depth of this layer is called the water table. The water table differ from place to place.
• The rainwater and water found in other sources like in rivers and ponds seeps through the soil and fills the empty spaces and cracks deep below the ground. The process of seeping of water into the ground is called as infiltration.
• The groundwater is recharged by this process. At places the groundwater is stored between layers of hard rock below the water table. This is called as an aquifer. Water from aquifers can be pumped out with the help of tube wells or handpumps.

Depliction of Water

• Water drawn from underground gets restored by seepage of rainwater.
• The water table does not get affected until we draw as much water as is replenished by natural processes. However, water table goes down if the water is not sufficiently replenished.

Reasons of depliction of Water

• Increase in population
• Industrial and agricluture activites
• Scanty rainfall
• Deforestation and decreased effective area for seepage of water

Increase in population

• Increasing population creates demand for construction of houses, shops, offices, roads and pavements.
• This decreases the open areas like parks, and playgrounds.
• This decreases the seepage of rainwater into the ground.

Increasing industries

• Water is used by all the industries resulting high consumption.
• The number of industries is increasing continuously. Water used by industries is generally drawn from the ground.

Agricultural activities

• Majority of farmers in India depend upon rains for irrigating their crops.
• Irrigation systems such as canals are there only in a few places.
• Eerratic rainfall creats lack of water required for crops.
• due to this reason,farmers have to use groundwater for irrigation.
• Population pressure on agriculture increasing day by day increase use of groundwater.

Distribution of Water

• At some places have good amount of rain and are water-rich. On the other hand, there are deserts which have very less rainfall.
• India is a vast country and the rainfall is not the equal everywhere.
• Some regions have excessive rains while some others have less rainfall.
• Excessive rains cause floods, whereas the absence of rains results in droughts.
• Therefore, some regions in India may have floods while others may suffer from droughts .

Water Managment

The rainwater can be used to recharge the groundwater. This is termed as water harvesting.

Bawri was one of the traditional way of collecting water. With time the bawris fell into disuse and garbage started piling up in these reservoirs. The bawris are being revived. Today the situation is that inspite of scanty rains these places are managing their water needs very well.

Drip irrigation is a modern technique of watering plants by making use of narrow tubings which deliver water directly at the base of the plant.