Precipitation: The millions of tiny droplets collide with one another to form larger droplets. When the air around the clouds is cool these drops of water fall in the form of snow or rain.

Evaporation: Water from oceans, lakes, ponds and rivers evaporates due to the heat of the sun.

There are two types of rain water harvesting
1. Collecting water from where it falls.
2. Collecting rainwater by constructing bunds.

Floating layer of ice acts as a protective coat and does not permit heat to escape from water. So aquatic animals manage to live in Arctic and Antarctic circle.

polar ice - gaps, glaciers and ice sheets in Arctic region and Antarctica.

The cold surface of the bottle containing icy water cools the air around it and the water vapour of the air condenses on the suface of the bottle. This process is also the result of condensation of water vapour.

wells, glaciers, rivers, lakes, ponds, etc.

(i) Sewage should not be disposed off in rivers or oceans before treatment.
(ii) If we dispose sewage water before treatment the river and oceans will be polluted.
(iii) We can not use the river water for our day to day life.
(iv) Aquatic animals and species will die due to pollution.

(i) "To a thirsty man, a drop of water is worth more than a sack of gold".
(ii) "Water covers 2/3 of the surface of the earth. But only 0.002% is drinkable".
(iii) "Save water to secure for your future".
(iv) "Store water for dry days".
(v) "Save water, Save life".

The main reasons for water scarcity
i) Population explosion
ii) Uneven distribution of rainfall
iii) Decline of ground water table
iv) Pollution of water
v) Careless use of water

(i) Direct collection and use of rain water is called rainwater harvesting.
(ii) Excellent and valuable source of water in emergencies.
(iii) Ideal solution for inadequancy of water.
(iv) Increase ground water level.
(v) Reduces rainwater run off and solves drainage problems in houses.

(i) Potable water is the water which is safe to drink. On an average the human body requires 2-3 liters of water per day for proper functioning.
(ii) It is transparent.
(iii) It is odourless and colourless.
(iv) Cleaned of harmful contaminants.
(v) It is harmless or free from disease causing bacteria.

When we breathe out, the hot air comes out from our mouth which condenses and gets changed into tiny water droplets and hence the glasses become wet.