Notes On Water : A Precious Resource - CBSE Class 7 Science
Availability of water Nearly 71% of the earth is covered by water in the form of oceans, seas, lakes, rivers, ice, ground water and moisture in the air. But most of it is not fit for human consumption. Water that is fit for human consumption is called freshwater. Only 0.006% of the water on the earth is actually available for our use.  In nature, water exists in three forms As a solid, it exists as icecaps at the poles, snow-covered mountains and glaciers. As a liquid, it is in the form of water in oceans, lakes and rivers, and underground water. Its gaseous form is the water vapor in the air around us. Water cycle or hydrological cycle The continuous cycling of water in nature that keeps the total amount of water on the earth constant is called water cycle. Processes involved in water cycle The processes involved in the water cycle are, evaporation, condensation ,precipitation and infiltration. Evaporation The process of conversion of water molecules into vapor  is called evaporation. water vapor collects in the sky in the form of clouds. Condensation The process of conversion of water vapor into water by cooling is called condensation. Precipitation Water falls from the sky in the form of rain, snow, hail, or sleet, this process is called precipitation. Infiltration The process of seeping of water into the ground is known as infiltration. Aquifer Sometimes, ground water accumulates between layers of hard rock. This is known as an aquifer. Water in aquifers can be drawn with tube wells and hand pumps. Water table The level below which the ground is saturated with water is called water table.   Ground water Ground water is the water found below the water table. Depletion of water table As long as the water drawn from the ground is replenished by seepage of rain water, the water table remains unaffected. The problem starts when we take more water from the ground than is replenished by natural means. Then the water table goes down, and it is said to have been depleted. Reasons for depletion of the water table Increasing population that creates more demand for water. More wells are dug and water is drawn from them. Industrial activities are increasing the demand for water. For example, the construction industry uses tube wells to draw ground water. An increase in agricultural activities demands more water. In areas where there are no streams and lakes, ground water is used for irrigation. Scanty rainfall is another reason for depletion of the water table. Water table depletion can be a result of deforestation. Water management Water management is the continuous matching of water resources with the water requirements of a place. Water management essentially involves activities that identify sources of water, prevent wastage of water, and implement recycling of water. It may also include treatment of water to make it suitable for human consumption. Prevent wastage of water Water leaking from pipes Fixing Leaking taps. Water over-flowing from buckets while clothes are being washed alongside Using water wisely while brushing the teeth, shaving, bathing, washing and during many other activities, practising rainwater harvesting. Conservation of water Instead of letting rainwater runoff into the sea, it can be used to recharge ground water. This is known as rainwater harvesting. Rainwater harvesting can be used to raise the water table in arid areas. It can also be used to create water storage areas. Farming, which typically requires huge quantities of water, can also benefit from good water management. Bawris This is the old method of rain water storage and recharge. In olden days people built deep step wells into the ground. These deep step wells are called bawris. During rainy season these wells are filled with water. The water is stored in these wells for longer time because they are very deep the evaporation of water is less. During shortage people use this water. Drip irrigation Drip irrigation is an economical way of using water. This technique involves the use of tubes to deliver water straight to the base of a plant, where it is taken up by the roots. Effects of water scarcity Plants need water to absorb nutrients from the soil and make their food. Without water, plants would die, and greenery would be lost. This, in turn, would mean the end of all life on the earth, because without plants, there would be no food, oxygen or rainfall. There would also be many other problems.

#### Summary

Availability of water Nearly 71% of the earth is covered by water in the form of oceans, seas, lakes, rivers, ice, ground water and moisture in the air. But most of it is not fit for human consumption. Water that is fit for human consumption is called freshwater. Only 0.006% of the water on the earth is actually available for our use.  In nature, water exists in three forms As a solid, it exists as icecaps at the poles, snow-covered mountains and glaciers. As a liquid, it is in the form of water in oceans, lakes and rivers, and underground water. Its gaseous form is the water vapor in the air around us. Water cycle or hydrological cycle The continuous cycling of water in nature that keeps the total amount of water on the earth constant is called water cycle. Processes involved in water cycle The processes involved in the water cycle are, evaporation, condensation ,precipitation and infiltration. Evaporation The process of conversion of water molecules into vapor  is called evaporation. water vapor collects in the sky in the form of clouds. Condensation The process of conversion of water vapor into water by cooling is called condensation. Precipitation Water falls from the sky in the form of rain, snow, hail, or sleet, this process is called precipitation. Infiltration The process of seeping of water into the ground is known as infiltration. Aquifer Sometimes, ground water accumulates between layers of hard rock. This is known as an aquifer. Water in aquifers can be drawn with tube wells and hand pumps. Water table The level below which the ground is saturated with water is called water table.   Ground water Ground water is the water found below the water table. Depletion of water table As long as the water drawn from the ground is replenished by seepage of rain water, the water table remains unaffected. The problem starts when we take more water from the ground than is replenished by natural means. Then the water table goes down, and it is said to have been depleted. Reasons for depletion of the water table Increasing population that creates more demand for water. More wells are dug and water is drawn from them. Industrial activities are increasing the demand for water. For example, the construction industry uses tube wells to draw ground water. An increase in agricultural activities demands more water. In areas where there are no streams and lakes, ground water is used for irrigation. Scanty rainfall is another reason for depletion of the water table. Water table depletion can be a result of deforestation. Water management Water management is the continuous matching of water resources with the water requirements of a place. Water management essentially involves activities that identify sources of water, prevent wastage of water, and implement recycling of water. It may also include treatment of water to make it suitable for human consumption. Prevent wastage of water Water leaking from pipes Fixing Leaking taps. Water over-flowing from buckets while clothes are being washed alongside Using water wisely while brushing the teeth, shaving, bathing, washing and during many other activities, practising rainwater harvesting. Conservation of water Instead of letting rainwater runoff into the sea, it can be used to recharge ground water. This is known as rainwater harvesting. Rainwater harvesting can be used to raise the water table in arid areas. It can also be used to create water storage areas. Farming, which typically requires huge quantities of water, can also benefit from good water management. Bawris This is the old method of rain water storage and recharge. In olden days people built deep step wells into the ground. These deep step wells are called bawris. During rainy season these wells are filled with water. The water is stored in these wells for longer time because they are very deep the evaporation of water is less. During shortage people use this water. Drip irrigation Drip irrigation is an economical way of using water. This technique involves the use of tubes to deliver water straight to the base of a plant, where it is taken up by the roots. Effects of water scarcity Plants need water to absorb nutrients from the soil and make their food. Without water, plants would die, and greenery would be lost. This, in turn, would mean the end of all life on the earth, because without plants, there would be no food, oxygen or rainfall. There would also be many other problems.

#### Activities

Activity 1 Southeastwater.com has created student interactive animation on “Water Cycle”. In this activity student build water cycle on their own using instructions. This activity is very useful for younger children. This activity also awoke hidden creativity in students. Go To Activity Activity 2 Discoveryeducation.com has created an interactive animation on “Ground Water”. In this activity students learn about ground water. Students will explore reservoirs of ground water and movement of ground water. Student can also learn more about depletion of ground water and more. Go To Activity Activity 3 Tn.nic has created a wonderful animation on “Rain Water Harvesting”. In this activity students learn about rain water collection in different types of roofs. This animation explains collection of rain and storage of rain water into tanks or infiltration of surface water into aquifers. This activity hepl to bring awareness in children. Go To Activity Activity 4 Schoolnet.lk has created an educational animation on “Drip Irrigation”. From this activity students learn about drip irrigation technology and how it enhance the crop yields. Student will explore different types of drip irrigation systems for different types of soils. Students can also learn more about advantages and disadvantages of drip irrigation. Go To Activity