NCERT Solutions for Class 4 EVS Chapter 13

The colour of the river water appears blue at the place where it begins.

The fishes need fresh and clean water. People throw their useless and waste materials into water due to this water become polluted. those places where water is polluted that place becomes unfit for fishes.

Before the river reaches the village, its water is clean and fresh. There are many fish in it and many other animals and birds come to it.

The colour of the water in the river changes when it reaches the city. This is because the industrial waste, the sewage and the garbage from the city are thrown into it, these things polluting it.

Yes, this is the river Yamuna in front of us. Water of river Yamuna is looks dark and it’s smell is very bad. This due to pollution.

I would like to live near the place from where the river begins because I can get fresh air and fresh water at that place.

I would like to remove the waste from the banks and in between water of the rivers. Because of these wastes river water is getting polluted.

Yes, I have seen people throwing flowers, ashes of dead humans, religious statues, etc. in river water. I have also seen some people living near the rivers throwing garbage in the river water.

First of all, we should spread awareness among People about the consequences of polluting water bodies and rivers. today we are facing a big problem of drinking water and this may become more difficult in future if we will not stop. for this all the people take care of this that no one should wash their clothes and bathe their animals in the river water. The sewage and the industrial waste should not be dumped directly into the river. Both sewage and the industrial waste should be first treated to remove the harmful chemicals and solid waste before dumping into rivers.

I would like to drink water at the upper reaches from the beginning of the river. The water near the source of a river is pure and uncontaminated.

Yes, I have seen the sea. I saw the sea in films also. Apart from that, I saw the sea when I was in Mumbai.

There is a river in my city and I often cross the river. I have been near a sea during my trip to Mumbai.

The water from the sea is not drinkable because it is very salty, which is not good for health.

In the summer season, the water level of the water bodies, such as river, pond or stream, decreases due to the evaporation of water but water of Himalayan rivers increases due to excess ice melt. In the rainy season, the water level of the water bodies rises. The water of the ponds in higher places freezes in the winter in places where the climatic conditions are very cold.

During the rainy season, the level of water in a river, pond or stream is at its maximum, while in the April and May the water level is at the minimum.

Yes, this is delhi city which is situated across the river Yamuna.

As I have seen, there is no change in summer and winter season because all the water in river Yamuna used for drinking purpose. The water flowing across Delhi is home and industrial waste. But in rainy season there is flood like situation and muddy water.

I have not seen any water animal in the river Yamuna across Delhi because water is polluted at drastic level.

There are different types of tree and plant on bank of river Yamuna. Some people growing vegetables and seasonal fruits around it.

There are several type of birds come where water clean. Some of them are Eagle, crow, swan, etc.

Yes, flood is common problem in India at time of rainy season. I have also seen flood in river Yamuna.

There is excess of water everywhere. Water enters even in houses. People suffer a lot.

Yes, I have seen dirty water in a rivers and in some ponds also.

Pure water is clean and clear. Dirty water is not so. Even if the water looks clean, it may not be alright to drink that water. It may contain germs that causes diseases.

No, oil may not dissolve in water. We can see oil floating over water.

Water can be cleaned by following different ways:
(a) By boiling the water
(b) By adding alum to water
(c) By adding chlorine to water
(d) By filtering water using water purifiers

at home we can purify water by different methods like, alum can be added to clean the water. Water is purified by the method of evaporation.

Rivers are important as-
• They carry sediments and minerals which are very useful for us
• They make the soil fertile by depositing the sediments and silt etc on the river banks.
• They provide a cheap and efficient inland transport for trade and commerce.
• They help cities and towns in carrying their wastes.
• Their water is widely used in irrigation and in developing hydroelectricity.
• They provide habitat and food for organisms
• Plays an important role in water cycle

Pollution is the addition of harmful materials into the environment. These harmful materials are called pollutants. It refers to any substance that harmfully impacts the environment or organisms that are living within the affected environment. The major types of pollution include: air pollution, water pollution, soil pollution and noise pollution.

Water pollution is the pollution of the water bodies, such as lakes, rivers, seas, the oceans, as well as groundwater. It takes place when the pollutants reach these bodies of water, without any treatment. Waste from homes, factories and other buildings get into the water bodies and the water gets contaminated

The rivers get polluted by-
• Throwing of some harmful substances in them
• Dumping sewage and other solid waste
• Opening the city drains into rivers
• Draining waste water of factories into rivers
• Plastic and metal can, bottles etc being thrown in water
• Poisonous substances like pesticides and fertilizers

The following measures should be taken to keep the river water clean-
 Do not litter or dump any kind of waste material in water
 Use less water at home to reduce burden 0n sewage treatment plants
 Use organic gardening to reduce the use of chemical fertilizers
 Create awareness about not washing clothes or bathing animals in the rivers.
 Maintaining sanitation around the water sources.

Sewage is that liquid waste which has water as its largest component along with various types of impurities like waste water from houses, offices, factories, hospitals etc.

Sewage treatment or the domestic wastewater treatment is a type of wastewater treatment which aims to remove the contaminants from sewage to produce an waste matter that is suitable for release to the surrounding environment thus preventing water pollution

Sea water is very salty. High amount of salt rapidly cause dehydration, loss of water in our body and in some cases cause death too. That is why sea water is unfit for drinking.

We should never drink water from a natural source directly whether it is a river or a lake as that is not purified, even if the water looks clean. Water in a stream, river or lake may look clean, but it can still be filled with dirt, germs like bacteria, viruses, and parasites that can result in waterborne diseases.

Water pollution is harmful for the aquatic animals too. Spreading of harmful substances such as oil, plastics, waste from factories and chemicals into water harms the aquatic animals. They can take in all these things through their skin or food and water intake and can die.

The colour of the water in the river changes when it enters the city, town or village. This happens because the industrial waste, garbage and sewage are thrown into it which make it highly polluted.

The level of the water in rivers and lakes is always changing due to inflows and outflows of water. The reason for this can be precipitation, overland runoff, groundwater seepage etc. So, the amount and location of surface water changes over time and space, whether naturally or with human help.

Any substance that dissolves or is added into a liquid is called a solute. Eg: salt, sugar

A liquid (water) in which the solute is added or dissolved is called a solvent. Eg: milk, water.

When a solute completely dissolves in a solvent and disappears, a solution is forms. Eg: salt and water when added make saline water solution.

The substances which do not mix with milk are fruit pieces, dry fruits. Such substances which do not mix in a liquid are called Insoluble substances. Eg: chalk powder, sand, pebbles, grass etc.

Water Purification is the process of removing undesirable and unwanted substances from water which contaminate the water. This method is followed especially for the purification or cleaning of drinking water to make it free of impurities and fit for consumption.

The different methods of water purification are-
 Boiling- It is one of the most effective method of purifying or cleaning water at home of all the impurities and germs and make water safe for drinking.
 Chlorination /Bleaching- By putting correct amount odf ch;orine or bleaching powder can also disinfect or purify water and make it fit for drinking. The chemicals kill the germs but they should be used in small quantity to avoid poisoning.
 Filtration- There are different ways to filter water at home-
i. Cloth filter- Use cotton or muslin cloth in case of extreme emergency although this method may not be very effective as it can remove only big sized impurities and not the smaller ones or germs.
ii. Commercial filters- They are highly successful in removing all the impurities from the contaminated water.

A few examples of commercial filters that are being used by us today are-
 Ceramic Candle Filters- eg. Pure it
 Reverse Osmosis (RO) – eg- Kent, Aquasure
 UV (Ultra Violet Filters) –eg-Aqua guard, Aqua fresh

The floods can be caused due to:
 Overflowing of water in rivers and streams
 Damage to dams, breaking of the walls of dams
 Coastal areas getting flooded due to Tsunami
 Heavy rainfall
 Deforestation
 Melting of snow and greenhouse effect
 Climatic changes
 Destroy bridges, highways, buildings etc
 Damage power house and
 Cause deadly water borne diseases

The floods cause widespread damage to crops, domestic animals, property and human life. During floods, many animals get carried away by the force of water and eventually die.

The floods can be controlled by-
 Planting more trees as trees help in controlling floods
 terrace slopes to reduce slope flow
 building man-made channels to divert water from flooding
 construction of dykes, dams, reservoirs or holding tanks to store extra water during flood periods.