NCERT Revision Notes for Chapter 16 Water: A Precious Resource Class 7 Science

Answer

• How much water is available?
• Water cycle
• Steps of water cycle
• Groundwater
• Depletion of water table
• Water management
• Reasons for scarcity of water

Answer

→ Earth’s surface is covered with about 71% of water.

→ Not all water is good for human consumption. The water fit to use is fresh water.

→ All water on the earth is contained in the seas and oceans, rivers, lakes, ice caps, as groundwater and in the atmosphere.

Answer

→ Water on earth can be maintained for millions of years by various processes which make water cycle.

• Water circulates in water cycle which is found in three forms. They are:

(i) Solid: Snow-covered Mountains and glaciers.

(ii) Liquids: Oceans, lakes, rivers and underground.

(iii) Gaseous: Water vapor in atmosphere.

Answer

→ It is also known as hydrologic cycle.

→ Water cycle describes the continuous movement of water on the surface or below the surface of earth.

→ The balance of water on earth remains fairly constant over time individuals water molecules can come and go in and out of the atmosphere.

Steps of water cycle:

I. Ground water

II. Evaporation

III. Condensation

IV. Clouds

V. Transpiration

VI. Infiltration

VII. Precipitation

Answer

→ Ground water is the large storage of water is inside the ground.

→ The water is located beneath the ground surface in soil pore spaces and in the fractures of rock formations.

→ Water table is the upper limit of layer.

→ Ground water is founds below the water table.

• Infiltration: It is a process of seeping of water into the ground is called infiltration.

• Aquifer: water which is stored between layers of hard rocks below the water table is called aquifer.

Depletion of water table

• If water is not sufficiently replenished then water table may go down.

• The reason is increasing population, industries, agricultural activities, decrease of seepage area for seepage of rainwater, deforestation and scanty rainfall.

Answer

→ Ground water that we get as rain fall just flows away. Rainwater is used to recharge the groundwater. This is referred to as water harvesting.

→ In India water storage and water recharge like the Bawris. It was the traditional way of collecting water.

→ Drip Irrigation is water saving Irrigation system. In this system, water falls on the roots of the plants drop by drop by the help of pipes.

→ We should turn off taps while bathing.

→ Map the floor instead of washing.

→ Use a bucket instead of bathtub.

Answer

→ Deforestation.

→ Uneven distribution of rainfall.

→ Scanty rainfall.

→Increasing industries.

→Increasing population rate.