NCERT 7th Class (CBSE) Science: Water: A Precious Resource

Question: Enlist some methods to conserve water.

Answer: Water conservation is process of preventing wastage of water, using water carefully and recharging ground water. Water conservation can be done by :-

1. Repairing leaking pipes and taps.
2. Not wasting water during brushing teeth, shaving, bathing, washing clothes and during other activities.
3. Rainwater harvesting.
4. By drip irrigation of plants.

Question: Why are we left only tiny fraction of water for use even if about 75 % of the earth surface is covered with water?

Answer: This is because most of the water about 97% of surface water is in sea and ocean as salty water that is unfit for domestic and agricultural use.

Question: Explain various processes that make up the water cycle.

Answer: There are six important processes that make up the water cycle:

Condensation: the opposite of evaporation. Condensation occurs when a gas is changed into a liquid.

Infiltration: Infiltration is an important process where rain water soaks into the ground, through the soil and underlying rock layers.

Runoff: Much of the water that returns to Earth as precipitation runs off the surface of the land, and flows downhill into streams, rivers, ponds and lakes.

Evaporation: the process where a liquid, in this case water, changes from its liquid state to a gaseous state.

Precipitation: When the temperature and atmospheric pressure are right, the small droplets of water in clouds form larger droplets and precipitation occurs. The raindrops fall to Earth.

Transpiration: As plants absorb water from the soil, the water moves from the roots through the stems to the leaves. Once the water reaches the leaves, some of it evaporates from the leaves, adding to the amount of water vapour in the air. This process of evaporation through plant leaves is called transpiration.

Question: What is a baoli?

Answer: Baoli or bawri is a structure which was used traditionally in India to store rainwater and recharge groundwater. Now-a-days it is voiced to revive this practice as a part of rain water harvesting.

Question: Why do we need the water cycle?

Answer: The Earth is covered by water, however, almost 97% is salt water found in the oceans. We cannot drink salt water or use it for crops because of the salt content. We can remove salt from ocean water, but the process is very expensive.

Question: Why water is considered as a precious resource?

Answer: Water is a precious source because all our daily activities are carried out with the help of water only. Water is found everywhere but not everywhere it is drinkable/ usable. Though the seas have no lack of water but still we can’t drink or use it anywhere. Water helps in nourishment of animals and plants. We can’t live without water and because it is scarce, that’s why water is precious.