Chapter 16 | Water | Class-7 DAV Science Solutions

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DAV Class- 7 Water Question and Answer

Something To Know

A. Fill in the blanks.

1. About 97% of water is present in oceans and seas.

2. Only 0.3 per cent of freshwater available for use is present in rivers, lakes and streams.

3. Groundwater is drawn from wells, tubewells and hand pumps.

4. Use of sprinkler and drip techniques for irrigation reduces wastage of water.

5. The network of pipes that carries wastewater to water treatment plant is called sewerage system.

B. Write True or False for the following statements.

Ans:

C. Tick the correct option.

1. Ocean water is unfit for drinking as it is-

Ans 1: very salty

2. ‘Rain water harvesting’ can help us to conserve-

Ans 2: rainwater

3. On the earth, the percentage of water, that is fresh and readily available for use, is, nearly-

Ans 3: 0.3%

4. One of the important factors, that can lead to a scarcity of water, is-

Ans 4: deforestation

5. Wastewater is also called-

Ans 5: sewage

D. Answer the following questions in brief.

1. Name the three forms in which water exists on the earth.

Ans 1: Ice (solid), Water (liquid) and water vapour (gas).

2. Give the meaning of the term ‘water table’.

Ans 2: The upper layer of groundwater is called the water table.

3. Name two methods of drawing out ground water.

Ans 3: Two methods of drawing out groundwater –

• Rehat or water wheel
• Stepwell/ tubewells

4. Name two activities which lead to the formation of sewage.

Ans 4: Washing clothes, Bathing etc.

5. State any two precautions that can help avoid the ‘choking of drains.

Ans 5: two precautions that can avoid choking of drains are –

• Do not throw solids, like left over food, leaves, cotton, polythene bags, etc., in the drains.
• Do not throw cooking oil, paints, chemicals, engine oil, in the drains.

E. Answer the following questions.

1. How is increase in population responsible for shortage of water?

Ans 1: Water is considered precious as it supports life on earth. With increase in population, demand for water has increased whereas its resources have depleted. This causes a shortage or scarcity of water.

2. Discuss, in brief, how ‘rain water harvesting’ can be done.

Ans 2: Rainwater harvesting should be done by collecting rainwater in underground tanks. This would help in replenishing the groundwater.

3. Discuss any two causes that lead to a decrease in ground water level.

Ans 3: two causes that lead to a decrease in groundwater level are:

• The amount of rainfall in most regions has decreased. This has happened due to many factors. Some of them are deforestation, increase in construction activity, etc.
• As the amount of rainfall decreases, farmers depend more on ground water for irrigation Hence, level of ground water is constantly decreasing.

4. How can ‘better management of water resources’ help in conservation of water?

Ans 4: Better management of water resources can help in conserving water. The rainwater should not be allowed to flow into drains. The use of sprinklers and drip irrigation techniques, for Irrigating the crops, can help in reducing wastage of water. Any broken, or leaking, the pipe should be immediately repaired or replaced.

5. Write, in brief, about the basic details and the role of the ‘sewerage system’.

Ans 5: just as a network of pipes brings clean water to our homes, a network of pipes takes the wastewater, or sewage, away. This network of pipes is called the sewerage system.

Role of the sewerage system

It carries the sewage, from its source to a wastewater treatment plant. The wastewater is cleaned, and purified, by various processes at these treatment plants. The water, thus, treated and cleaned, is then allowed to mix with river or seawater.