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Chapter 14

Water

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Chapter 14 Science Class 6 teaches students about one of the major necessities for the survival of living organisms on earth: Water. The importance of water, its various natural and man-made sources, its misuse and its conservation methods have been discussed thoroughly. The concept of the water cycle is also explained in this chapter. Processes like evaporation, transpiration and condensation are discussed in terms of the water cycle. The concepts of rain, flood and drought are mentioned briefly.

Topics Covered in this Chapter
  1. How much water do we use?

  2. Where do we get water from? 

  3. Water cycle

  4. Loss of water by plants 

  5. How are clouds formed?

  6. Back to the oceans

  7. What if it rains heavily?

  8. What happens if it does not rain for a long period?

  9. How can we conserve water?

1. What is water?

Water is one of the fundamental and essential natural resources required for the existence of living organisms on the earth. Two-thirds of the total earth’s surface is covered by water. Therefore, it is present in an adequate amount. 

Chemically, water is a molecule made up of 2 elements: hydrogen and oxygen in a 2:1 ratio. The molecular formula of water is H2O. Physically, water is odourless, transparent, colourless and tasteless.  Biologically, water is an essential component to run the daily metabolic activities of living organisms. In fact, 70% of the human body is made up of water. Plants need water for food production, i.e., for photosynthesis.  

We all can live without food for months, but without water, we cannot survive even for days. Even plants dry out and die without water.

2. How much water do we use?

  • Directly or indirectly water is a part of every aspect of our daily life. From giving life to a living thing to being used in the making of a non-living thing, water is required everywhere. 
  • Water is used in all our daily household activities from drinking, cooking, bathing, and brushing to wiping floors, cleaning toilets, and washing clothes. On an average, a human consumes almost 600 to 700 litres of water a day. 
  • Water is an essential element for the agriculture and industrial sectors as well. 
  • Despite covering two-thirds of the earth’s surface, only 2% of the total water is suitable for drinking purposes.

Where do we get water from?

There are many sources of water:

Surface water: Two-thirds of the earth's surface consists of seas, oceans and other water bodies, but most of it is salty water unfit for daily use. It has salts, impurities and toxins that can cause health issues. The 2% available water used for drinking and other purposes comes from lakes, ponds, rivers and wells. 

Rainwater: The water cycle brings back the ocean and seawater into the river, wells, and lakes in the form of rain. 

Glaciers: When a glacier melts it adds to the water bodies.

Groundwater: Water found underground in the cracks and spaces between the soil, rock and sand is called groundwater. The water reservoir of the ground is maintained through rain and water bodies like wells.

3. Water cycle

The water cycle is a natural phenomenon that involves a cyclic process: continuous movement of water from the earth’s surface to the atmosphere and from the atmosphere back to the earth’s surface. The water cycle or the circulation of water on the earth's surface and in the atmosphere is also called the hydrological cycle.

The 4 processes involved in the water cycle are:

Step 1: Evaporation

This is the first stage of the water cycle when water from the oceans, seas and other sources heats up due to direct sunlight and evaporates in the form of water vapours.

Step 2: Condensation

Water vapours in the clouds cool down to form water droplets during condensation. 

Step 3: Precipitation

When water vapours cool down to form water droplets they fall on the earth’s surface in the form of snow or rain known as precipitation.

Step 4: Collection of rainwater

Rainwater gets collected as groundwater and also goes back into the water bodies.

4. Loss of water by plants

Plants absorb water from the roots, they use this water for making food and retain some of it. The rest of the water losses through the leaves and stems in the atmosphere in the form of water vapours. This process of loss of water through leaves and stems is called transpiration. 

5. How are clouds formed?

Clouds are formed by the process of condensation.

Condensation: As we go higher from the earth’s surface, the air becomes cooler; the cold temperature of the air condenses the water vapours present in the air into water droplets. These water droplets appear as clouds when seen from the earth’s surface. When these droplets form in an excessive amount, they come back on the earth in the form of rain and snow.   

6.  Back to the oceans

Do you ever wonder what happens to the water that comes in the form of rainfall and snowfall? Earth's surface is above sea level; therefore, most of the water from rain and snow sooner or later goes back to the oceans and seas. 

There are many ways in which water returns to the oceans:

  1. Snow from the mountains melts and reaches the streams and the rivers. Some of the rainwater also directly falls into the streams and the rivers.
  2. The streams and the rivers later on merge into the oceans and the seas. Some of the water from rivers also flows into the lakes and the ponds. 
  3. A major part of rainwater goes into the ground. Groundwater can be excessed through wells, tube wells and handpumps. 
  4. Open wells get filled with groundwater. Lakes and ponds also receive water from the ground.

Over-exploitation of groundwater is worrisome. In areas with less or no vegetation, rainwater flows quickly and takes away the upper fertile layer of the soil with it.
Nowadays, people are making land concrete, this reduces the seepage of rainwater into the ground, creating groundwater shortage.

7. What if it rains heavily? 

The duration, time, and amount of rainfall differ from place to place. Some parts of the world receive rainfall throughout the year, whereas some receive for a few days.  In India, most of the rainfall occurs during the monsoon season. The sowing of many crops depends upon the amount of rainfall. However, excess of anything is harmful. Heavy rains may lead to a rise in the level of water in rivers, ponds and lakes. This may cause floods in many areas leading to crop destruction, death of street animals, and loss of property and human life.

8. What happens if it does not rain for a long period?

Too little rain or too much of it can cause disasters. If there is no or little rainfall, the soil of that region becomes dry because of evaporation and transpiration. The water levels in the ponds and wells of that region also dry up leading to scarcity of groundwater as well. This may result in a natural calamity called drought. 

9. How can we conserve water?

Only 2% of the total available water is fit for drinking and other purposes, the rest of the water in the water bodies is unfit for human use. When the groundwater level decreases drastically, it cannot be used further. This further decreases the suitability and availability of water. With the increase in the population, the demand for natural resources like water is also increasing. However, we have to keep in mind that these resources are limited and are extremely important for our survival. 

Therefore, we have to stop the exploitation of water resources and start thinking of water conservation:

Rainwater harvesting is a successful technique of conserving water. It involves the collection and storage of rainwater for use rather than letting it go off the drains. It can be done in two ways: 

  • Rooftop rainwater harvesting: Rainwater that falls on the rooftop is collected into a water tank through pipes. This water needs to be filtered before it is used for household purposes. The water can also be let to go directly into the pit in the ground so that it seeps into the soil to refill the groundwater.
  • Water collected in drains: Several roadside drains collect water; we can allow that water to go into the ground directly. 

MSVGo is a one-stop solution to enhance your knowledge and understanding of the subject at a very affordable price. All the topics of Class 6 Science are effortlessly explained on the MSVGo app. We provide notes, videos, numerous practice questions, and NCERT solutions for each chapter from Class 6 to Class 12. Download the MSVgo App for free and kickstart your journey of becoming a champ.

What is the toughest topic in water? 

Although this chapter is easy to comprehend, it introduces students to new scientific processes like evaporation and condensation. Therefore, it might take some time for students to learn them. 

From where do we find the exercise solutions of this chapter?

The exercise solutions can be found on the MSVGo app.

How does rainwater become saline?

When rainwater falls on the earth’s surface, it gets mixed up with common salts and other minerals and substances present on the different layers of the earth, rocks and water bodies and becomes salty. 

What is Evaporation?

The physical process of changing liquid into a gas is called evaporation. It is a natural phenomenon. Water evaporates to become water vapours. In the water cycle, evaporation happens at the surface of water bodies in the presence of the sun's heat. The water at the surface of seas, oceans, lakes etc. is constantly evaporating due to the sun's heat. This evaporated water goes into the atmosphere and forms clouds, which again burst to fall on the earth’s surface as rainwater leading to a continuous water cycle.

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