Revision Notes of Ch 16 Water: A Precious Resource Class 7th Science
- How much water is available?
- Water cycle
- Steps of water cycle
- Groundwater
- Depletion of water table
- Water management
- Reasons for scarcity of water
How much water is available?
→ 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.
Water Forms
→ 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.
Water cycle
→ 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
Groundwater
→ 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.
Water management
→ 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.
Reasons for scarcity of water:
→ Deforestation.
→ Uneven distribution of rainfall.
→ Scanty rainfall.
→Increasing industries.
→Increasing population rate.
NCERT Solutions of Water: A Precious Resource Class 7