Water — Practice

Question 1

What percentage of the Earth's water is found in oceans and seas?

Accepted Answer

About 97 per cent, and it is saline.

Question 2

What does saline mean?

Accepted Answer

Containing dissolved salt, as sea water does.

Question 3

What is an aquifer?

Accepted Answer

A porous layer of rock underground in which water is stored.

Question 4

Name the four stages of the water cycle in order.

Accepted Answer

Evaporation, condensation, precipitation and collection.

Question 5

How much of the Earth's water is fresh, and where is most of it held?

Accepted Answer

Only about 3 per cent is fresh water, and most of that is frozen in glaciers and ice caps, leaving a very small share reachable in groundwater, rivers and lakes.

Question 6

Why is underground water free from suspended impurities?

Accepted Answer

Because it is naturally filtered as it seeps down through layers of soil, sand and rock, which trap mud and sand.

Question 7

Define desalination and state its main drawback.

Accepted Answer

The artificial process of converting sea water into fresh water by removing the salt. Its drawback is that it needs a great deal of energy and is therefore expensive.

Question 8

Through which three materials is harvested rainwater usually filtered, and where does it then go?

Accepted Answer

Through sand, gravel and charcoal. It is then stored in a tank or allowed to seep into the ground through a recharge pit.

Question 9

Water from a new borewell is clear. Is it therefore safe to drink? Explain.

Accepted Answer

Not necessarily. Natural filtration removes suspended impurities such as mud and sand, which is why it looks clear, but it does not remove dissolved salts, fluoride, arsenic or germs. The water should be tested before anyone drinks it.

Question 10

Why was rainwater harvesting made compulsory for buildings in Tamil Nadu?

Accepted Answer

Because groundwater was being pumped out faster than rain could replace it, so the water table fell and wells dried up. Harvesting sends roof runoff back into the ground and helps refill it.

Question 11

A student says the Earth is running out of water. Correct this using the water cycle.

Accepted Answer

The Earth's water is never used up, because the water cycle circulates it endlessly. What is short is water that is fresh, clean and reachable, since about 97 per cent is saline and most of the rest is frozen.

Practice — Water

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