7 Science Chapter 16 Water A Precious Resource

Chapter Notes and Summary
• Water is most essential natural material for human beings, plants and animals.
• Water exists as snow or frost in solid state, as normally available in liquid state and as steam or water vapour is gaseous state.
• various sources of water are : oceans (seas), rainwater, groundwater, rivers and lakes. This comprises nearly three-fourth part of earth’s surface.
• Water is maintained on earth by various processes which make water cycle, still there is shortage of water at many places due to many human activities.
• upper limit of underground water is called water table.
• process of seepage of water into ground is called infiltration.
Water cycle : Ocean is biggest store house of water which on evaporation forms clouds and which after condensation falls down as rain. After rain, it is passed through rivers and gets collected again in ocean. circulation of water in this manner is known as water cycle. cycle is also performed through living beings like absorption and transpiration of water by plants and drinking by animals. Animals loose water during respiration and perspiration. They also loose water through excretion.
Fig. Water Cycle
Groundwater : water of rain or from other sources like ponds, which sweeps or percolate under ground and collects over impermeable rocks is called groundwater.
• At places, groundwater is stored between layers of hard rocks below water table. This is known as aquifer.
• Scanty rainfall, increasing population, increasing industries, agricultural activities and deforestation are some of causes for depletion of water table at some places.
• Wastage of water should be avoided. Besides recharge of water to ground should be strengthened. Rainwater harvesting technique should be used to recharge groundwater.
• Drip irrigation process of watering plant should be started in farms.
• In order that water is available to future generation, we should use it economically.

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