WHAT ARE WATER POLLUTANTS?

WHAT ARE WATER POLLUTANTS?

In Class VII you learnt that water is a precious resource. Think and list the various activities in which we need water. We saw that water is becoming scarce due to the increase in population, industries and agricultural activities. You have also studied how water becomes “dirty” after we use it for washing clothes, bathing, etc. This means that we are adding some materials to the water, which spoil its quality and change its smell and colour.

Whenever harmful substances such as sewage, toxic chemicals, silt, etc., get mixed with water, the water becomes polluted. The substances that pollute water are called water pollutants.

Activity 18.5:

*  Try to collect samples of water from a tap, pond, river, well and lake.

*  Pour each into separate glass containers.

*  Compare these for smell, acidity, and colour.

*  Complete the following Table

Table 18.2:

Source: This topic is taken from NCERT TEXTBOOK

HOW DOES WATER GET POLLUTED? – CASE STUDY

HOW DOES WATER GET POLLUTED? – CASE STUDY

Ganga is one of the most famous rivers of India (Fig. 18.7). It sustains most of the northern, central and eastern Indian population. Millions of people depend on it for their daily needs and

Figure 18.7: Course of the river Ganga

livelihood. However, recently a study by the World Wide Fund for Nature (WWF) found that Ganga is one of the ten most endangered rivers in the world. The pollution levels have been rising for many years. We have reached this stage because the towns and cities, through which the river flows, throw large quantities of garbage, untreated sewage, dead bodies, and many other harmful things, directly into the river. In fact the river is ‘dead’ at many places where the pollution levels are so high that aquatic life cannot survive.

An ambitious plan to save the river called the Ganga Action Plan was launched in 1985. It aimed to reduce the pollution levels in the river. However, the increasing population and industrialisation have already damaged this mighty river beyond repair. Now, the Government of India has launched a new initiative known as National Mission for Clean Ganga (NMCG) in 2016.

Let us take a specific example to understand the situation. The Ganga at Kanpur in Uttar Pradesh (U.P.), has one of the most polluted stretches of the river (Fig. 18.8). Kanpur is one of the most populated towns in U.P.

Figure 18.8: A polluted stretch of the river Ganga

People can be seen bathing, washing clothes and defecating in the river. They also throw garbage, flowers, idols of gods and goddesses and non-biodegradable polythene bags into the river.

At Kanpur, the amount of water is comparatively small and the flow of the river is very slow. In addition, Kanpur has more than 5000 industries. These include fertiliser, detergent, leather and paint industries. These industrial units discharge toxic chemical wastes into the river.

Based on the above information think of the answers to the following questions –

*   What are the factors responsible for the pollution of the river?

*   What steps can be taken to restore the river Ganga to its past glory?

*   How would the disposal of garbage, etc., affect the living organisms in the river?

Many industries discharge harmful chemicals into rivers and streams, causing the pollution of water (Fig. 18.9). Examples are oil refineries, paper factories, textile and sugar mills, and chemical factories. These industries cause chemical contamination of water. The chemicals released include arsenic, lead, and fluorides which lead to toxicity in plants and animals. There are regulations to prevent this. Industries are supposed to treat the waste produced before discharging it into waters, but quite often the rules are not followed. The soil is also affected by impure water, causing changes in acidity, growth of worms, etc.

We have learnt in Chapter 1 the importance of pesticides and weedicides for the protection of crops. However, all these chemicals dissolve in water and are washed into water bodies from the fields. They also seep into the ground to pollute groundwater.

Have you seen ponds which look green from a distance because they have a lot of algae growing in them? This is caused by excessive quantities of chemicals which get washed from the fields. These act as nutrients for algae to flourish. Once these algae die, they serve as food for decomposers like bacteria. A lot of oxygen in the water body gets used up. This results in a decrease in the oxygen level which may kill aquatic organisms.

Figure 18.9: Industrial waste discharged into a river

Activity 18.6:

*   You had investigated the sewage disposal system of your locality in Class VII.

*   Do you remember how the sewage was collected from your home and where it went thereafter?

Sometimes untreated sewage is thrown directly into rivers. It contains food wastes, detergents, microorganisms, etc. Can groundwater get polluted by sewage? How? Water contaminated with sewage may contain bacteria, viruses, fungi, and parasites which cause diseases like cholera, typhoid and jaundice.

The bacteria present in the faeces of mammals are indicators of the quality of water. If water has these bacteria, it means that it has been contaminated by fecal matter. If such water is used by us, it can cause various infections.

Hot water can also be a pollutant! This is usually water from power plants and industries. It is released into the rivers. It raises the temperature of the waterbody, adversely affecting the animals and plants living in it.

Source: This topic is taken from NCERT TEXTBOOK

WHAT IS POTABLE WATER AND HOW IS WATER PURIFIED?

WHAT IS POTABLE WATER AND HOW IS WATER PURIFIED?

Activity 18.7:

*   Let us construct a water filter with simple, everyday materials.

*   Take a plastic bottle and cut it into 2 halves at the centre. Use the upper half as a funnel by putting it upside down in the lower half.

*   Make layers in it with paper napkin or a fine cloth followed by, cotton, sand and then gravel.

*   Now pour dirty water through the filter and observe the filtered water.

*   Discuss the following questions amongst yourselves and with your teacher:

      a.  Why do we need to filter water before drinking?

      b.  Where do you get your drinking water from?

      c.  What will happen if we drink polluted water?

Boojho is very upset. He tells Paheli that he drank water which looked clear and was without any smell, but still he fell sick!

Paheli explains that water which looks clean may still have disease-carrying microorganisms and dissolved impurities. So, it is essential to purify water before drinking, for example, by boiling.

Water which is suitable for drinking is called potable water. You have seen how various physical and chemical processes in the sewage treatment plants help to clean water before discharging it into water bodies. Similarly, municipal bodies treat the water before supplying it to households.

25% of the world’s population is without safe drinking water!

Let us see how water can be made safe for drinking:

*   You have already seen how water is filtered. This is a physical method of removing impurities. A popular household filter is a candle type filter.

*   Many households use boiling as a method for obtaining safe drinking water. Boiling kills the germs present in the water.

*   Chlorination is a commonly used chemical method for purifying water. It is done by adding chlorine tablets or bleaching powder to the water. We must be cautious. We should not use more chlorine tablets than specified.

Source: This topic is taken from NCERT TEXTBOOK

WHAT CAN BE DONE?

WHAT CAN BE DONE?

Activity 18.8:

*   Investigate the level of awareness about water pollution in your area.

*   Collect data on the sources of drinking water and the methods of sewage disposal.

*   What are the common water-borne diseases in the community?

*   You can consult your local doctor/health worker for this.

*   Which are the governmental and non-governmental organisations working in this field?

*   What are the measures being taken by them for generating awareness?

Laws for industrial units should be strictly implemented so that polluted water is not disposed off directly into rivers and lakes. Water treatment plants should be installed in all industrial areas (Fig. 18.10). At our individual levels, we should consciously save water and not waste it. Reduce, reuse, and recycle should be our mantra!

Figure 18.10: Water treatment plant

Think of your daily routine – how can you save water?

We can think of creative ideas like reusing water used for washing and for other household tasks. For example, water used for washing vegetables may be used to water plants in the garden.

Pollution is no longer a distant phenomenon. It is affecting the quality of our daily lives. Unless we all realise our responsibility and start using environment-friendly processes, the very survival of our planet is in danger.

While brushing your teeth, leaving the tap running may waste several litres of water. A tap that drips once every second wastes a few thousand litres of water every year. Think about it! 

Source: This topic is taken from NCERT TEXTBOOK