It's importance and source

Water is the "elixir" of life, without water the planet earth would have not been a living planet.
It is because of the presence of water ; the earth look blue in space and is called as "blue" planet.
The earth is the only planet which has been able to withhold water ,because of its force of gravity and overall temperature range.
Lakes, rivers and oceans are most visible form of water and are termed as SOURCE WATER.
But water we usually use comes from the surface ,termed as "GROUND WATER".
HYDROGEOLOGY is the study of underground water while the study of surface water comes in preview of HYDROLOGY and the expert of this fields are called HYDRO GEOLOGIST and HYDROLOGIST respectively.
The mechanics of water or fluid comes under HYDRAULICS or FLUID MECHANICS.
Human beings had instinctive awareness about the existence of groundwater from the very beginning of their civilisation.
They have used it's natural emission in cave ,springs ,oases and marshes and had also made structures to tap and (NIMES,QANATS),some of them still in use.
Theoretically water form by combination of one oxygen and two hydrogen ions through electrovalent bonding.

CHEMISTRY AND PHYSICS OF WATER

The water molecules in turn are linked with each other by hydrogen bond.
The bipolarity and presence of hydrogen bond account for it's being the best solvent and surface tension properties which produces capillary action in soil.
A droplet of water contains 1,700,009,000,000,000 water molecules.
At or near the earth surface the prevailing temp. and press. conditions are just right to permit water to exit largely as liquid water.
The earth is unique where water can exist in all the three state and 0.01C and 0.00603 atmospheric pressure, all the phases can coexist.
If we go on by using different permutations and combinations oh hydrogen and oxygen isotopes together then we can have hundreds of compositions of water molecules.

The origin of water is ascribed to the degassing of mantle which took place during the early part of the earth's geo-history .
The volcanic activity takes place , the dissolved gases are released in the atmosphere and there hydrogen and oxygen combine to form water vapour which in turn get condensed to form water and come down on the earth surface as snow or rain and are known as METEROIC WATER.
The magma generated in the mantle or asthenosphere when move up and solidifies inside the earth.
Water form at an appropriate temperature by chemical combination of (OH) ions giving rise to JUVENILE WATER.
Water collected on the surface of earth in ponds, lakes, river, sea and oceans are together called surface water.
Water which seeps down the earth surface is called as subsurface water. The ground water is a part of subsurface water.
A part of subsurface water perhaps even much below the groundwater trapped in rocks called as CONNATE WATER.
These water are highly salty owing very high dissolved content because of its very old age. It is also knows as salt brine or fossil water ,encountered usually when drilling for oil and gas is carried out.