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CBSE Class 7 Chemistry Notes- Chapter 5 Water

About 71% of earth’s surface is covered in water but most of it cannot be consumed as it is in the oceans and seas. The water in the oceans and seas is too salty to be consumed. Only the freshwater available in rivers and lakes is fit for consumption. Freshwater is about 0.006% of the total water and even this water is being quickly used up.
Water exists in all three forms:
(i) Solid: As snow and ice in the glaciers and ice caps
(ii) Liquid: In oceans, seas, rivers, lakes, groundwater
(iii) Gas: As water vapour in the atmosphere
The continuous cycle of water among its three forms is called water cycle
Water seeps into the ground through the process of ‘infiltration’ and gets stored as ground water. The upper limit of ground water is called the water table.
Depletion of water table
 Ground water is drawn and used for everyday purposes. Excessive usage of ground water leads to depletion of water table. The major reasons for depletion of water table are:

  • Increasing population
  • Increasing industries
  • Agricultural activities

The distribution of water is uneven due to climatic conditions and uneven rainfall,
We have limited amount of water available and therefore it must be managed carefully. It is important to follow practices such as rain water harvesting, drip irrigation, etc. so as to save water.

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