Important Notes for CBSE Class 7 Science Chapter 16 – Water: A Precious Resource. Water: A Precious Resource Class 7 Notes and Study Material Download in PDF form.
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Water: A Precious Resource Class 7 Notes
World water day is celebrated on 22nd March to create awareness about saving water.
According to the United Nations on an average one individual requires about 50 liters of water per day.
Safe and clean water is a scanty natural resource.
In many areas there is shortage of water and people have to wait in long ques to fetch water.
It is proposed that if not used consciously about one third of the world population will face water shortage.
HOW MUCH WATER IS AVAILABLE?
- Earth’s 71% surface is covered with water bodies.
- These waterbodies include seas, oceans, rivers, lakes, ice caps etc.
- This water is not potable for drinking or daily use.
- Less freshwater is available for drinking.
FORMS OF WATER
- Water cycle is an important process.
- It helps in keeping water in sufficient amount on the surface of the earth.
- In the water cycle, water can be available in any of 3 forms i.e., solid, liquid
and gas at a given time or place.
- In the solid state, water is in form of snow or ice, which is present as ice caps or snow-covered mountain tops or glaciers.
- Water of oceans, lakes, rivers is in liquid state.
- Water vapors are present in the air aroundus.
- Water keeps on changing its form and, in this way, the total amount of water on the planet is always constant.
- Civic bodies in urban towns make use of well-maintained watersupply system.
- A number of villages do not have this facility and have to walk many kilometers to get potable water.
- Mostly women and children suffer a lot due to this.
- people can make use of wells, tube wells or hand pumps as well.
GROUNDWATER AS AN IMPORTANT SOURCE OF WATER:
1.) If the soil in a particular area is moist, it indicates presence of ground water.
2.) As one goes deeper in the earth’s crust, all space between soil and gaps between rocks is filled with water.
3.) Water table is the topmost layer of the water between soil and gaps between rocks.
4.) The water tableis different at different places, apart from this it may be deep or quite shallow.
5.) Ground water is found below the water table and is generated from trickling of rainwater, river and pond water into the soil.
6.) Infiltration is the draining of water in soil and recharging groundwater water.
7.) An aquifer is a groundwater reserve between 2 layers ofhard rock below the water table.
8.) This water can be retrieved by tube wells or handpumps.
DEPLETION OF WATER TABLE:
1.) Recharging of water table is an essential process.
2.) The levels of water in the table are maintained by seeping of rainwater by natural process.
3.) Increase in population, construction of roads, less rainfall,deforestation, industrial andagricultural activities are factors affecting water table.
4.) Consumption of ground water has drastically increased over the years due to use in construction, industries etc.
- Agricultural activities:
1.) Irrigation is still not quite popular in India in agriculture.
2.) In area where rainfall is scanty cannels can be constructed, but it may still not be a reliable method if the rainfall is not sufficient that year.
3.) Use of ground water has increased leading to depletions in water table.
DISTRIBUTION OF WATER:
- The distribution of water on the planet is varied due to difference in rainfall in different parts of the planet.
- If the density of rainfall is high in a particular area it may lead to flood.
- On the other hand, if there is less rainfall it may lead to draught like conditions.
WATER MANAGEMENT:
1.) It is a very important practice.
2.) In many areas well planned network of pipes is used for water supply, where as some problems may arise due to leakage of water.
3.) In this case civic authorities should take immediate action to prevent water loss.
4.) Due to daily activities of individuals a lot of water is wastage.
5.) Apart from this leaking tap in households, free flowing rain water leads to water loss.
6.) Rain water can be used to replenish the ground water by rainwater harvesting.
7.) Conventional water retention practices like using bawris should be promoted.
8.) In agriculture, farmers can make economic use of water by making use of drip irrigation to water the field.
WHAT ROLE YOU CAN PLAY
1.) If any taps are leaking call plumbers to repair the leakage.
2.) Turn off the water supply or taps while brushing
3.) Use mops to clean the floor.
4.) Practice rain water harvesting.
EFFECT OF WATER SCARCITY ON PLANTS
- Due to lack of water the potted plant may die or wilt away.
- Water is essential for the transport of nutrients in plants.
- If plants are not able to survive, it will disturb the food chain and life on the planate will be depleted.
- Apart from food scarcity, lack of oxygen and rain will also occur.