Water Notes 6th Science Lesson 14 Notes in English

6th Science Lesson 14 Notes in English

14] Water

Introduction

• Water is one of the basic substance 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.

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 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/town.
• For example Ramu says he and his family get water from the pipes in washrooms and kitchens. Sankar says he has to use hand pump daily both in the morning and evening to collect the water.
• Raja says his mother used to get up early and walks to pond to get water. Where do you get water for your household uses?

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 ice bergs and ice caps on top of tall mountains, galaciers 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.

Availability of water

• We know that nearly 3/4th of the surface of the earth is occupied by water.
• Most of the water, that is 97% of the total amount of water that exits on earth is found in seas and oceans.
• Can we drink the water available in the sea?
• Sea water is salty. But water used for our daily purposes is not salty.
• It is known as fresh water.
• Water obtained from ponds, puddles, river, tube-wells and taps at home is usually fresh water.
• If the total water on earth be 100%, let’s see what percent would be the availability of fresh water.
• 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 of water is not readily available for drinking.
• The distribution of the totally available (3%) freshwater is as follows:

1. Polar ice caps and glaciers 68.7%
2. Ground water 30.1%
3. Other sources of water 0.9%
4. Surface water 0.3 %
5. The distribution of total 0.3% of surface water is as follows:
6. Lakes 87%
7. Rivers 2%
8. 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?
• 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.
• Water freeze at 0o Celsius at normal pressure. Every year march 22nd is observed as the world water day.

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 upto 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.

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 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.

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 atmosphere has water vapour?

• Let us do the following activity…
• Natural Sources of fresh water
• Three types of natural sources of fresh water are available on the earth.

Surface water

• Water present on the surface of the earth such as river,lake,ponds, streams or fresh water 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 is 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.,

The Himalayas

• 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 rivers.

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 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, it the existence of aquatic animals.

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 reserviors is measured in TMC/feet. Water released from dams is measured in cusec (cubic feet/sec).

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 ground watertable
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:

1. Bringing awareness about the bad effects of throwing wastes into the water bodies
2. Recycling of water by separating pollutants.
3. Minimizing the use of chemical fertilizers in agriculture. It reduces the pollution of underground water.
4. Controlling deforestation
5. 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.

• (e.g): Collecting water from the roof tops of the houses or buildings (Roof water harvesting).

b. Collecting flowing rain water

• (e.g): Collecting rainwater by constructing ponds with bund.

Importance of water

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

Swamps

• 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.

Water distribution and treatment system

• We know that water is distributed by local bodies.
• In some areas which water is obtained from river, lake and ground water is treated and distributed.
• Model of water distribution and treatment plant is shown in figures.