Clear, transparent water is not always fit for drinking as it may have many disease carrying microbes and dissolved impurities that are not visible to unaided eyes. So, transparent water also needs to be purified by various processes.

P is carbon monoxide, Q is haemoglobin R is oxygen and S is carboxyhaemoglobin.

We can take the following steps to restore river Ganga:
(i) Industries are supposed to treat the waste produced before discharging it into the water.
(ii) Pesticides and weedicides should not be allowed to flow into the river. (Hi)Untreated sewage should not be thrown directly or indirectly into the river.

If we drink polluted water, we may be affected from diseases such as cholera, typhoid, and jaundice as the polluted water contains many pathogens.

Water can be made safe for drinking by following ways:
(i) Water is filtered. Many filters available in the markets are used by people.
(ii) Some use boiling as a method for obtaining safe drinking water because boiling kills the germs present in the water.
(iii) Chlorination is a chemical method for purifying water.

Nitrogen is not a greenhouse gas. It is naturally found in the air and is a major constituent of it.

Clear air contains about 78% nitrogen and 21% oxygen

Untreated or inadequately treated sewageis major source of groundwater pollution. Sewage contains food wastes, detergents, microorganisms, etc which seeps into the ground to pollute groundwater.

The bacteria present in the faeces are used as indicators of the quality of water.

Kanpur city is situated at the bank of the river Ganga. Many people can be seen bathing, washing clothes, throwing garbage, idols of Gods, nonbiodegradables polythenes. In addition, Kanpur has more than 5000industries. They discharge toxic chemical waste into the river. Hence, Kanpur really makes the Ganga polluted.

We should plant trees and nurture the ones already present in the neighbourhood. This is to
(i) Reduce air pollution Plants clean the air. They also reduce dust particles in the air. This will lower down the pollution level
(ii) Minimise global warming The greenhouse gas CO₂ is responsible for global warming. Plants utilise CO₂ for making food and give out O₂, Therefore, planting more trees will reduce the CO₂ in atmosphere and thus global warming will be in control.

Some preventive measures of water pollution are :
(i) Sewage should be treated properly before discharging it into nearby rivers.
(ii) Water treatment plants should be installed in all industrial areas.
(iii) The use of excessive fertilisers and pesticides should be avoided.
(iv) Laws for industrial units should be strictly implemented.
(v)We should consciously make efforts at individual level to conserve water.