Water Class 6 Notes

WATER

• It is one of the most important resources for us. The three-fourth part of the earth is composed of water near about 71%.
• Almost 97% of water is salty found in the oceans. However, we need freshwater to survive which is only 3 %, and in that 3%, 2% freshwater is found in glaciers and ice caps completely frozen.
• About 0.6% of freshwater is present deep under the ground from the total water present on earth.
• About 0.009% of freshwater is found in rivers, lakes and springs from the total percentage of the water.

SOURCES OF WATER

We can get water through many sources such as:-

Rainwater

• It is one of the important sources of collecting freshwater(Figure 1).
• Rainfall occurs due to the process called the water cycle in which the water evaporates from vapours, and these vapours condense to form again water.
• The water comes back to the ground again. But during this process, the rainwater mixes with many impurities which makes it polluted.
• However, rainwater is always found in the purest form of water.

Figure 1: Rainfall.

Groundwater

• Almost 30% of freshwater is found under the ground.
• The rainwater goes deep down under the ground by getting filter through the various layers of the soil such as clay, sand and gravel and collected there.
• We get this freshwater through hand pumps, wells and tube wells(Figure 2).

Figure 2: Getting underground water by hand pumps.

Surface Water

• We use almost 80% of freshwater that comes from the surface.
• The main source of water coming to the surface is rain and sometimes the melting of snow.
• Rivers, lakes, ponds and streams water are called surface water.

Ice Caps and Glaciers

• The water is found in the frozen phase at the top of the mountains called glaciers.
• These glaciers have the purest form of water. When they melt, the water goes down the hill and mixes with many impurities(Figure 3).

Figure 3: Glaciers.

Ocean Water

• Almost 97% of the water comes from the ocean, but this water is salty(Figure 4).
• The main source of getting water from the oceans is rivers because rivers join the oceans.
• The formation of the common salt by the process of evaporation takes place in seas and oceans.

Figure 4: Ocean.

USES OF WATER

• The important functions of the body like digestion and excretion required water to work properly.
• The roots of the plants carry water that contains several nutrients dissolved in it. Later, transferred to the whole plant.
• Water is also responsible for the regulation of the human body temperature. It helps to excrete the waste in the form of urine and sweat.
• Growing crops on a large scale required water in a large scale called irrigation(Figure 5).

Figure 5: Irrigation
• Due to the capability of dissolving substances more than any other liquid, water is also called a universal solvent.
• Water is used for daily home works like cooking, bathing, washing and cleaning.
• Water is used as fire extinguisher.
• The formation of products like fabric, soaps, and medicines need water.
• Water is used to generate electricity by creating dams. Such electricity is called the hydroelectricity.

STATES OF WATER

Water can be found in the three states:-
i. When it gets 0°C temperature, the water converts into ice. This process is called freezing.
ii. On heating the water, when the temperature reaches up to 100°C, it changes into a gaseous form called the water vapours. this process is called vapourisation.
iii. On cooling, the water vapours change into liquid form. This process is called condensation.
iv. When water boils, it changes into a gaseous state below its boiling point. This process is called evaporation.
All these process are interchangeable with each other(Figure 6).

Figure 6: Interconversion of states of water.

SPECIAL PROPERTIES OF WATER

There are some unique properties of water such as:-
• The molecules of water expand while freezing, but the other liquids contract when they freeze. Therefore, soft drinks and water bottles are not kept in the freezer for a long time because they can burst.
• The solid-state(ice) of the water is lighter than its liquid state because of the lesser density. While the other liquids solid form is heavier than their liquid form. Ice molecules are arranged in a cage-like structure surrounded by a lot of empty spaces called voids. As the molecules of ice are not closely-packed, ice can float in the water.

WATER CYCLE

It is a physical process in which water interchangeably undergoes all its three states(Figure 7).
The following processes take place during the water cycle are:-
i. Firstly, the water of the oceans and rivers evaporates to form water vapours. This process is called evaporation.
ii. Secondly, these water vapours rise to the sky and form clouds where they condense to the liquid state again. This process is called condensation.
iii. Thirdly, when the accumulation of water vapours inside the clouds increases, then the size of the clouds also increases.
iv. Lastly, these water vapours can be found in three forms inside the clouds such as rain, snow and sleet known as precipitation which fall back to the ground.

DROUGHTS

• Rainfall is the main source of getting water. During the summer season, the weather conditions start becoming hot. As a result, the process of evaporation and transpiration frequently increased which causes the loss of water.
• Due to some reason, rain does not occur for a long time causes a shortage of water. Moreover, the water of lakes, ponds and rivers start drying. This leads to a condition or disaster called drought(Figure 8).

Figure 8: Drought.
This also creates a shortage of food due to the death of animals and plants. Such regions where the drought condition is present for over many years lead to the shortage of food called famine.

FLOODS

• It is an opposite condition of drought where excessive rainfall filled water all over the surface(Figure 9).
• This flooded condition blocks the roads, railway lines and even airlines due to lightning dangers.
• It also disrupts the sewage system in which the water contains impurities that lead to several life-stricken diseases such as typhoid, hepatitis A, and cholera, etc.
• It destroys crops and lands, which can cause a shortage of food.
• It contaminated water and landscape by carrying hazardous materials and mix them with fresh-stored water.
• It creates an epidemic situation in a particular area by increasing the percentage of people getting infected with a particular water borne disease.

Figure 9: A flooded city.

WATER POLLUTION

When hazardous materials are mixed with the water, it gets polluted. There are many ways in which water gets polluted such as:-
• Waste comes out from the factories(Figure 10).
• Using chemical fertilisers, insecticides and pesticides washed and moved with the rainwater.
• Throwing garbage in rivers, lakes and ponds.
• Doing daily works of a home near the water bodies such as washing clothes and bathing
• Littering on the beach. The waves carried the garbage with them.

WATER CONSERVATION

The water can be conserved in the following ways:-
• Do not waste excessive amount of water while bathing, washing, cleaning and mopping.
• Avoid leaving taps open to control unnecessary flow of water.
• Use buckets to store the showering water while bathing and use it to watering plants.

Dams

• A barrier constructed to raise the water level to form a reservoir behind it called dam(Figure 12).
• The main work of the dam is to retain water while the floodgates prevent the water flow in specific lands or areas.
• Electricity is produced on a large scale by dams.
• During drought conditions, the floodgates are open to flow the stored water in the reservoir, whereas in heavy rainfall, excess water is stored in the reservoir.

Figure 12: Dam.

Rainwater Harvesting

The collection of the rainwater and used it when it’s necessary is called rainwater harvesting. The following ways of collecting the rainwater are(Figure 13):-
• Roof-top rainwater harvesting is one of the methods in which the rainwater is collected in the tanks with the help of pipes of the rooftop buildings.
• The tanks placed on the roofs can collect the water while raining. Later, this rainwater transferred to the underground storing blocks through the pipes.

Figure 13: Rainwater Harvesting.
Also Read

• Notes
• NCERT Solutions

Practice Question

Question 1 What is $\frac {1}{2} + \frac {3}{4}$ ?
A)$\frac {5}{4}$
B)$\frac {1}{4}$
C)$1$
D)$\frac {4}{5}$
Question 2 Pinhole camera produces an ?
A)An erect and small image
B)an Inverted and small image
C)An inverted and enlarged image
D)None of the above

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