Water is essential for life: Water is very important in our daily life.
It is used for drinking, bathing, cooking, and washing clothes.
Apart from these, it is used for agriculture, industry and for construction of buildings.
It also plays an important role in the generation of electricity.
Natural sources of water: The natural sources of water are lakes, ponds, rivers and oceans.
Rain is the main sources and it is in pure form.
For drinking, well water is better than tank water.
As the rain passes through different layers of soil, the salt present in the soil dissolve in it.
Hence water in the well is either sweetish or salty.
Water cycle: When wet clothes are spread in sun's heat, the water content in them evaporates into atmosphere.
Similarly the water in lakes, wells and rivers evaporates into atmosphere due to the heat of the sun.
Then its vapors travel through the atmosphere gets cooled and condensed into small drops of water.
These drops join together to form clouds.
When the air around the clouds cools, the heavy drops fall to earth in the form of rain.
This rain again flows into tanks, wells and rivers.
Thus, in nature, water evaporates and form clouds.
These clouds bring rain.
This transformation is called 'water cycle'.
This is a continuous process in nature.
Sea water is salty: In some areas where it passes through layers of soil, large quantities of salts get dissolved in water.
So it becomes salty.
Such water is called salt water or saline water.
The dissolved salts and minerals pass into the sea through the rivers.
That is why the sea water is saltiest and unfit for drinking.
Generally the sea contains 3 to 5% of dissolved salts.
In some seas the percentage of salts is much more than 20% and the density of water is very high.
Dead Sea: This sea is near Palestine.
In this sea the salt content is as high as 27%.
The quantity of salt dissolved in water is calculated to be about 40 million tons.
Because of this extreme saltiness, no animal can live in this sea.
Its density keeps swimmers afloat.
We will not drown even if we jump into this sea.
Uses of water:

• Growth of plants
• Agriculture
• Production of electricity

Constituents of water: It contains oxygen and Hydrogen.
Each molecule of water contains two atoms of hydrogen and one atom of oxygen.
Properties of water: In ordinary state water is a liquid.
Pure water is colorless, odorless and tasteless.
It has the property of dissolving many substances like salts, minerals and gases in it.
Since it contains some amount of dissolved oxygen, fishes and aquatic plants can live in water.