These DAV Class 7 Science Notes and DAV Class 7 Science Chapter 16 Notes – Water act as excellent revision resources, particularly in preparation for board exams.
Water Class 7 DAV Notes
→ Water on Earth:
- Nearly three-fourth of the surface of earth is covered with water.
- About 97% of total water on earth is present in oceans and seas. This is saline water and hence is unfit for human consumption.
- 3% of total water on earth is available in the form of freshwater.
- 2% of total water is available in frozen form in glaciers and ice-caps.
- 0.7% of total water is available as groundwater.
- 0.3% of total water is available as surface water; in rivers, lakes and streams.
- Groundwater and surface water make 1% of total water, which is available for human consumption.
→ Local Sources of Water:
Water is supplied by the water supply system in cities. In villages, people take water from rivers, ponds, wells and tube-wells.
→ Groundwater and Water Table: Most of the rainwater and water from rivers seep through the soil and goes under the ground. This water is trapped in the space between the underground rocks. The upper level of this water is called water table. The water below the water table is called groundwater.
→ Scarcity of Water: People in most of the places face acute shortage of water. Due to increased human activities, forests have been cleared on large scale and new constructions have come up. This has disturbed the natural process of recharging the groundwater. Growing human population has resulted in an ever increasing demand for potable water. There is a mismatch between demand and supply for potable water. As a result, water scarcity is a major problem in modern times.
→ Water Management and Rainwater Harvesting:
Rainwater should be collected in underground tanks and allowed to seep under the ground. This practice is called rainwater harvesting. Rainwater can also be collected in tanks so that it can be used for daily needs.
Use of sprinklers and drip irrigation helps in conservation of water.
Unnecessary cutting of trees should be stopped. More trees should be planted.
We should follow these steps to conserve water:
Turn off the tap while brushing your teeth.
Leaking tap should be immediately repaired.
Plants should be water with a mug instead of a pipe.
→ Wastewater Management:
The water which flows in the drain from our houses is called wastewater. The wastewater is called sewage. Sewage goes into the sewerage system through which it is finally flown into a nearby waterbody.
→ Wastewater should be treated before being flown into the nearest waterbody. This is important from two angles. Treated wastewater is safer for aquatic animals and plants and is safe for human beings also. Treated wastewater can be used for many useful purposes; especially for irrigation.
→ Our Role in Wastewater management:
- Reduce the quantity of wastewater being produced from our homes.
- Do not throw solids; like food, leaves, cotton, polythene bags, etc. in the drains.
- Do not throw cooking oil in the drains.
- Do not throw chemicals; like paints, medicines, engine oil, etc. in the drain.
→ Rainwater harvesting: Collection of rainwater for future use or for recharging the groundwater is called rainwater harvesting.
→ Wastewater: The water flowing down the drain is called wastewater.
→ Sewage treatment plant: The plant where wastewater is treated to get rid of harmful impurities.
→ Potable water: Water which is fit for human consumption.
→ Groundwater: Water present below the surface of earth.
→ Sewage: Wastewater from homes, offices and other human establishments.
→ Water table: The top level of groundwater is called water table.