Water

Class 6 | Science — Chemistry | Unit 2

Class 6 Unit 2 Science

Unit 2. Water

Learning Objectives

• To recognize the sources and availability of water
• To clarify the composition of water and the process of water cycle
• To develop skills in suggesting ways to conserve water
• To realize the importance of water for life on earth
• To appreciate the efforts made to conserve water

Introduction

Water is one of the basic substances present in the earth. It plays a vital role in the evolution and survival of life. It is impossible to imagine life on the earth without water. Water helps to regulate the temperature of our planet. It also helps to maintain the temperature in organisms.

2.1 Where do we get water from?

We need water to perform several day to day activities like cooking food, washing clothes, cleaning utensils etc. We get water from different water sources in our surroundings. In villages or towns wells, canals, tanks, ponds, rivers, water tanks, hand pipes are the main sources of water.

List out the sources from where you get water in your village or town.

For example, Ramu says he and his family get water from the pipes in washrooms and kitchens. Sankar says he has to use a handpump daily both in the morning and evening to collect the water. Raja says his mother used to get up early and walk to the pond to get water.

Where do you get water for your household uses?

2.2 Where and how water is found on the earth?

Water is available in nature in three forms Solid, Liquid, Vapour.

Solid form of water - Ice - It is present in icebergs and ice caps on top of tall mountains glaciers and polar regions.

Liquid form of water - water - It is present in oceans, seas, lakes, rivers and even underground.

Gaseous form of water - Vapour - It is present in the air around us.

2.3 Availability of water

We know that nearly three fourths of the surface of the earth is covered by water. Most of the water that is 97 % of the total amount of the water that exists on earth is found in seas and oceans. Can we drink the water available in the sea? Seawater is salty. But Water used for our daily purpose is not salty. It is known as fresh water. Water obtained from ponds, puddles, rivers, tube-wells and taps at home is usually freshwater.

If the total water on earth were 100%, let's see what percent would be the availability of freshwater. Look at the pie chart given below.

From the pie chart, it can also be noted that 97% water is saline water. Only 3% found is the freshwater and that too in polar ice caps and glaciers. So, this portion water is not readily available for drinking.

The distribution of the totally available freshwater is as follows:

• Polar ice caps and glaciers 68.7%
• Ground water 30.1%
• Other sources of water 0.9%
• Surface water 0.3%

The distribution of total surface water is as follows:

• Lakes 87%
• Rivers 2%
• Swamps 11%

Thus, the above pie chart explains that we have a very small amount of fresh water available for human usage and so maintaining the water table and the conservation of water is very essential. Isn't it?

Do You Know?

Water while passing through layers of soil dissolves salts and minerals to a maximum extent. These salts and minerals have been deposited in seas and oceans for millions of years and are still being deposited. In addition, the oceanic volcanoes which are present inside, also add salts to the sea. Water with large amounts of dissolved solids is not potable or suitable for drinking. Such water is called saline water.

Activity 1. Relative amount of water at various sources

Take 20 litres of water in a bucket, a 500 ml mug, a 150 ml tumbler and a 1 ml spoon. If the capacity of the bucket is 20 litres, then it represents the total amount of water present on the Earth. Now, transfer a mug of water from the bucket and it is 500 ml and then it represents the total amount of fresh water present in the Earth. The water left in the bucket represents seas and oceans. This water is not fit for human use. The water present in the mug represents the freshwater which is present in frozen form on snow-covered mountains, glaciers and polar ice caps. This water is also not readily available for human use. Next, transfer 150 ml of water to the tumbler, from the 500 ml mug. then it represents the total amount of groundwater. Finally, take one-fourth spoonful of water while the capacity of the spoon is 1 ml, then it represents the total amount of surface water that is water seen in all the rivers, lakes and ponds of the world. It can be taken as potable water. When such a small amount of potable water is available, then we should be more economic in using water. Is it not?

Activity 2. Conduct the activity with common salt, sand, chalk powder, charcoal powder and copper sulphate. Fill up the following table.

Substance	Dissolves in water	Does not dissolve in water
Common Salt
Sand
Chalk Powder
Charcoal Powder
Copper Sulphate

From the above activity we could observe that common salt and copper sulphate dissolve in water and contribute their properties like colour and other properties to water but sand, chalk powder and charcoal powder do not dissolve in water.

2.4 Composition of Water

Water is a transparent, tasteless, odourless and nearly colourless chemical substance. It is composed of two atoms of hydrogen combined with one atom of oxygen. The molecular formula of water is H2O. However, the physical composition of water changes from place to place. It can be clear or cloudy, oxygenated or not very oxygenated and it can be fresh or salty. The amount of salt in water is termed as salinity. Based on its salinity water is classified into three main categories such as freshwater, brackish water and sea water. Fresh water contains 0.05% to 1% of salt. Brackish water contains up to 3% of salt and seawater contains more than 3% of salt. Ocean water is composed of many substances. The salts include sodium chloride, magnesium chloride and calcium chloride

Do You Know?

WATER FREEZE AT ZERO DEGREE CELSIUS AT NORMAL PRESSURE. EVERY YEAR MARCH 22 IS OBSERVE AS THE WORLD WATER DAY

Activity 3. Water contains dissolved salts

Take some tap water in a china dish and heat it. Continue heating till all the water gets dried up. Stop the heating and look at the china dish. What do you observe inside the China dish? Deposits of some solid particles on the surface of a china dish can be observed. The deposit is of salts that are dissolved in water. This shows that water has dissolved salts in it.

Note: Do not use distilled water or water from purifiers or R.O. (Reverse Osmosis) unit and the like for this activity.

2.5 Water Cycle

The water on the earth evaporates into the atmosphere due to the heat of the sun. The water vapour in the atmosphere forms clouds. From the clouds water falls on the earth in the form of rain or snow. By this natural process, water gets renewed. This is called the water cycle. Water cycle is a continuous process. It involves three stages evaporation, condensation and precipitation. It is also called the hydrological cycle.

Evaporation: Water from oceans, lakes, ponds and rivers evaporates due to the heat of the sun.

Condensation: Water vapour which enters into the atmosphere by evaporation moves upward with air, gets cooled and changes into tiny water droplets that form clouds in the sky.

Precipitation: The millions of tiny droplets collide with one another to form larger droplets. When the air around the clouds is cool these drops of water fall in the form of snow or rain.

Activity 4. Spread a piece of wet cloth in the sunlight. Observe after some time.

Where has the water in the wet cloth gone?

The water evaporates into the atmosphere due to the heat of the sun.

Have you heard of transpiration? It is the process of loss of water from the aerial parts of a plant in vapour form. There is a continuous cycling of water and it exists in three forms in nature. Water evaporating from lakes, rivers and oceans forms the gaseous state. Rain water forms the liquid state. Snow on mountains and polar ice caps forms the solid state. These three states occur in nature, keep the total amount of water on the earth constant even when the whole world is using it!

How do you know that the atmosphere has water vapour?

Activity 5. Condensation of water vapour

Take a glass half filled with water. Wipe the outer surface of the glass with a clean piece of cloth. Add some ice into the water. Wait for one or two minutes. Observe the changes that take place on the outer surface of the glass. From where do water drops appear on the outer side of the glass? The cold surface of the glass containing icy water cools the air around it and the water vapour of the air condenses on the surface of the glass. This process is also the result of condensation of water vapour.

2.6 Natural Sources of freshwater

Three types of natural sources of freshwater are available on the earth.

Surface water Water present on the surface of the earth such as river,lake,ponds, streams or freshwater wetland is called surface water.

Frozen water Water that is present in the frozen form as polar ice-caps and glaciers are called frozen water. A larger portion of water is 68.7% of the total available fresh water in frozen state.

Ground water Ground water is the water present beneath Earth's surface in soil. This water is obtained through springs, open wells, tube wells, or hand pumps etc.,

Do You Know?

The Himalayas, contain ice caps, ice bergs and glaciers. Ten of Asia's largest rivers flow from the Himalayas and more than a billion people's livelihoods depend on those river

More to know:

Water is measured in litre and millilitre. Gallon is also a measure of volume of liquids. 1 Gallon = 3.785 litre. Water level in the reservoirs is measured in TMC (One thousand million cubic feet). Water released from dams is measured in cusec (cubic feet per sec)

Do You Know? Aquatic animals

During winter, water in lakes and ponds in the cold countries will be frozen and a solid layer of ice is formed on the surface of water. Still aquatic animals living under the ice do not die. This is because the floating layer of ice acts as a protective coat, and doesn't permit heat to escape from water. So as the water at the surface alone turns to ice, lets the existence of aquatic animals.

2.7 Conservation of Water

There is no change in the total quantity of water available on the earth. It remains the same. But the water useful for plants, animals and man is decreasing day by day. It is called scarcity of water.

What are the reasons for scarcity of Water?

The main reasons for water scarcity

1. Population explosion
2. Uneven distribution of rainfall
3. Decline of groundwater table
4. Pollution of water
5. Careless use of water

We should take care to prevent scarcity of water. Otherwise, it is impossible for organisms to live on the earth. The only method of preventing scarcity of water is conservation of water. Saving water for the future generations by using water carefully and in a limited way is conservation of water.

Methods of water conservation:

Mainly, two methods can be followed for the conservation of water.

1. Water management

Water management consists of the following factors:

• a. Bringing awareness about the bad effects of throwing wastes into the water bodies
• b. Recycling of water by separating pollutants.
• c. Minimizing the use of chemical fertilizers in agriculture. It reduces the pollution of underground water.
• d. Controlling deforestation
• e. Adopting drip irrigation and sprinkler irrigation in agriculture. By this way lesser amount of water can be used for the irrigation

2. Rainwater harvesting

Direct collection and use of rain water is called rainwater harvesting. There are two types of rainwater harvesting.

a. Collecting water from where it falls. example Collecting water from the rooftops of the houses or buildings (Roof water harvesting).

b. Collecting flowing rain water example Collecting rainwater by constructing ponds with bund

Do You Know?

Coovam is an estuary! Estuaries are wetlands where water bodies meet the sea. It is a combination of fresh water from land meeting the salty seawater. Estuaries are home to unique plants and animal species.

2. 8 Importance of Water

In Human body: water in all cells, organs and tissues helps regulate body temperature and maintain other functions. On an average, the human body requires 2 to 3 litres of water per day for proper functioning. Water helps in digestion of food and removal of toxins from the body.

Domestic uses: Apart from drinking, people use water for many other purposes. These include cooking, bathing, washing clothes, washing utensils, keeping houses and common places clean, watering plants, etc

Do You Know

Swamps are wetlands that are forested. They occur along large rivers or on the shores of large lakes. The water of a swamp may be freshwater, brackish water or seawater. Swamps are important for providing fresh water and oxygen to all life. Pichavaram Mangroves in Chidambaram, Muthupet mangrove wetland. Pallikkaranai wetland in Chennai, Chembarambakkam in Kancheepuram are a few examples of swamps in Tamilnadu.

Agriculture: Water is also essential for the healthy growth of farm crops and farm stock and is used in the manufacture of many products.

Industry: Industry depends on water at all levels of production. It is used as a material, a solvent and for generating electricity.

Activity 6. Estimation of water consumed by a family on a day.

Activity	Amount of water used (in litres)
Brushing
Bathing
Washing clothes
Toilets
Cooking
Washing utensils
Cleaning floor
Any other purpose
Total amount of water used by a family in a day

Points to remember

• Water is one of the most important components that all animals including human beings and plants depend on for their livelihood.
• To an extent of 97% of the total water that exists on Earth is found in seas and oceans.
• Only 3% of the freshwater is available in polar ice caps and glaciers.
• Lakes, rivers, swamps constitute only 0.3% of the surface water.
• The moisture in the soil indicates the presence of underground water.
• The continuous circulation of water in nature is called the water cycle. It is effected by evaporation, condensation, precipitation and transpiration.
• Ground water is the water present beneath Earth's surface in soil.

ICT Corner

Water

Through this activity you will be able to know what happens to water when it is taken out of nature, into our house and once it leaves our houses.

Step 1: Type the URL or scan the QR code to launch the activity.

Step 2: A page of 3 games will open, click on the first game 'Melbourne water cycle', and click the "Play the Melbourne water game" button to start the game.

Step 3: Play the game by following the instructions and using the navigation keys. Observe the steps of water usage and the process of recycling the used water.

Step 4: Play the other two games to know about the Natural water cycle and Sources of water.

Simple Circuit's URL: https://www.educationsoutheastwater.com.au/resources?audience=&keywords=&topic=&yearLevel=&type=online-game

Evaluation

Exercise 1. Choose the appropriate answer

1. Around 97% of water available on earth is _____ water.

a. fresh b. pure c. salty d. Polluted

2. Which of the following is not a part of water cycle?

a. evaporation b. condensation c. rain d. Distillation

3. Which of the following processes add water vapour to the atmosphere?
1. Transpiration
2. Precipitation
3. Condensation
4. Evaporation

a. 2 and 3 b. 2 and 4 c. 1 and 4 d. 1 and 2

4. About 30% of the freshwater is found in?

a. glaciers b. ground water c. other sources of water d. surface water

5. Using R.O (Reverse Osmosis) plant at home eliminates a lot of non-potable water. The best way to effectively use the expelled water of RO plant is ______

a. make the expelled water go and seep near the bore well b. use it for watering plants c. to drink the expelled water after boiling and cooling d. to use for cooking as the water is full of many nutrients Exercise 2. Fill in the blanks

1. Only percent of natural water is available for human consumption.

2. The process of changing water into its vapour is called .

3. is built on rivers to regulate water flow and distribute water.

4. Water levels in rivers increase greatly during .

5. Water cycle is also called as .

Exercise 3. True or False. If False, give the correct statement 1. Water present in rivers, lakes and ponds is unfit for use by human beings . 2. Seas are formed when the water table meets the land surface. 3. The evaporation of water takes place only in sunlight. 4. Condensation results in the formation of dew on grass. 5. Sea water can be used for irrigation as such. Exercise 4. Match the following

1. Flood
2. Surface water
3. Sun light
4. Cloud
5. Frozen water

Options: Lake, Evaporation, Water vapour, Pole, Increased rainfall

Exercise 5. Arrange the following statements in correct sequence 1. These vapours condense to form tiny droplets of water. 2. The water droplets come together to form large water droplets. 3. The heat of the sun causes evaporation of water from the surface of the earth, oceans, lakes, rivers and other water bodies. 4. The large water droplets become heavy and the air cannot hold them, therefore, they fall as rains. 5. Water vapour is also continuously added to the atmosphere through transpiration from the surface of the leaves of trees. 6. Warm air carrying clouds rises up. 7. Higher up in the atmosphere, the air is cool. 8. These droplets floating in the air along with the dust particles form clouds. Exercise 6. Analogy

1. Population explosion: Water scarcity: Recycle :

2. Ground water: Surface water: lakes

Exercise 7. Give very short answer

1. Name four different sources of water

2. How do people in cities and rural areas get water for various purposes?

3. Take out a cooled bottle of water from the refrigerator and keep it on a table. After sometime, you notice a puddle of water around it. Why?

4. We could see clouds almost every day. Why doesn't it rain daily?

5. Name the places where water is found as ice.

6. How do aquatic animals manage to live in the Arctic and Antarctic Circle?

7. What are the types of rainwater harvesting?

Exercise 8. Give short answer

1. Differentiate between surface water and groundwater.

2. Write a few slogans of your own on the topic "Save Water".

3. About 71% of earth's surface is covered with water, then why do we face scarcity of water?

4. Give reason for the following statement – Sewage should not be disposed of in rivers or oceans before treatment.

5. Give the reasons, why water scarcity is in India? Explain .

Exercise 9. Answer in detail

1. What is potable water? List down its characteristics.

2. Who is known as the waterman of India? Browse the net and find the details about the award the waterman received for water management. State the findings by drafting a report.

3. What is rainwater harvesting? Explain in a few sentences how it can be used in houses.

Exercise 10. Question based on Higher Order Thinking Skills

1. When there is no pond or lake in an area, will there be formation of clouds possible in that area?

2. To clean the spectacles, people often breathe out on glasses to make them wet. Explain why the glasses become wet.

Exercise 11. CROSSWORD

DOWN

1. A method of water conservation.

2. Process of getting water vapour from seawater.

6. Water stored in dams is used for generation of

ACROSS

3. is a large body of non-potable water found in nature.

4. In summer, the body loses water as .

5. Plants undergo and contribute to the water cycle.

Exercise 12 (1). Observe the given graph carefully and answer the questions.

a. What percentage of water is seen in fish?

b. Name the food item that has the maximum amount of water in its content.

c. Name the food item that has the minimum amount of water in its content.

d. Human body consists of about _____ percentage of water.

e. Specify the food item that can be consumed by a person when he or she is suffering from dehydration.

Exercise 12 (2). Look at the map of Tamilnadu showing annual rainfall and answer the questions given below

a. Identify the districts that get only low annual rainfall in Tamilnadu.

b. Identify the districts that get a medium annual rainfall in Tamilnadu.

c. State the districts that enjoy high annual rainfall in Tamilnadu.

📝 Summary

1. Water is one of the basic substances on Earth that plays a vital role in the evolution and survival of life, helping to regulate temperature of our planet and maintain temperature in organisms.
2. Water exists in nature in three forms: solid (ice in icebergs, glaciers, and polar regions), liquid (in oceans, seas, lakes, rivers, and underground), and gaseous (vapor in the air around us).
3. Nearly three-fourths of Earth's surface is covered by water, with 97% being saline water in seas and oceans, and only 3% being freshwater.
4. Of the 3% freshwater available, 68.7% is in polar ice caps and glaciers, 30.1% is groundwater, 0.9% is from other sources, and only 0.3% is surface water from lakes, rivers, and swamps.
5. Conservation of water is essential because we have a very small amount of fresh water available for human usage, making it crucial to maintain the water table and conserve this precious resource.