CBSE Class 6 Chemistry Notes- Chapter 5 Water

                            CHAPTER 5 WATER
 
Water is one of the most basic needs of humans. We need water not just for drinking but also for a number of other purposes like bathing, cooking, cleaning, etc.
Our very survival depends on water. Trees and crops use water to grow and they give us food.
 
Water cycle
Water cycle is a cyclic process through which water evaporates from the surface of the earth, reaches the atmosphere and then cools down to form clouds and then falls back to the surface.
Plants lose water by the process of transpiration. Tis releases water vapour into the air. In addition to this, water from the oceans and seas evaporates as it gets heated up by the sunlight. All this water vapour rises into the atmosphere.
As it goes higher into the atmosphere, it cools down and forms clouds. These clouds are nothing but tiny droplets of water. These droplets combine to form bigger drops of water which sometimes become so heavy that they start falling. This is what we call rain. Water can sometimes also fall in the form of hail or snow. This happens when the water gets so cold up in the atmosphere that it converts into solid form.

The rain or snow falls on the surface of the earth. It may fall on either on land or on water bodies like oceans, seas, etc. When it falls on the land, it gets absorbed by the ground. This adds up to the ground water which is either available in open wells or is drawn up by a hand pump or tube well.

This movement of water from the surface of the earth to the atmosphere and then back to the surface is called Water Cycle.
 
Droughts and floods
In some areas, rainfall is very less. But sometimes this lack of rainfall may continue for a very long period of time which may cause droughts. Drought is a long period of time characterized by abnormally low rainfall due to which there may be a shortage of water.
However, excessive rainfall is also not favourable. If there is abnormally more rainfall, the water level of water bodies like rivers and lakes increases. This may cause dry land to submerge in water. This is called flood.

Conservation of water
With the increasing population, the supply of water is decreasing every day. Although two-thirds of the earth’s surface is covered in water, most of it is in the oceans and seas. This is salt water and cannot be used for every day purposes. We have a very limited amount of fresh water supply due to which there is a shortage of water in many parts of the world. This makes it important to conserve water.

Rainwater harvesting
Rainwater harvesting is a way to conserve rain water. In order to make sure that rain water is not wasted, we can collect it. This is called rainwater harvesting. Rainwater can be collected and stored to be used later.
Rainwater can be harvested from rooftop and through pipes, it reaches the storage tanks. This water can be used for various household activities like washing clothes & utensils, cleaning and after filtering, it can be used for drinking and cooking as well.
Rainwater can also be allowed to go directly into the ground from drains that run along the side of the road.