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|
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?
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:
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: