Introduction and Sources of  Water:

• Water is essential for the survival of all the living beings on earth.
• Water is not only essential for the survival but also used in industrial applications such as coolant, solvent, for steam generation, for air conditioning and fire fighting etc.
• Chemically water is a Compound, having one atom of Hydrogen and two atoms of Oxygen, with the Molecular Formula, $$H_{2}$$ O.
• It is a Polar Solvent and is considered as an Universal Solvent.
• It conducts Electricity due to its self ionization.
• The hybridization is SP$$^{3}$$ for water molecule, with Oxygen as the central atom containing two lone pairs due to lone pair - lone pair repulsion's, the bond angle changes to $$ 104^{\circ} 5^{'}$$ and the shape to bent shape.

Water Technology :

• The process of removing of all types of impurities from water and making fit for domestic or industrial purposes is called Water Technology or Water Treatment.
• Water is used for many purposes. It is used for drinking, industries, agriculture domestic purposes etc.

Important Sources of Water :

1. Surface water
2. River Water
3. Lake Water
4. Rain Water
5. Sea Water
6. Underground Water
7. Spring and Well Water

1. Surface Water :

• This water flows on the surface like rivers, streams, lakes, ponds and reservoirs. It contains suspended matter and often contains disease producing bacteria.
• This water is used for domestic and industrial Purposes.

2. River Water :

• Water from rain and spring water flow over the surface of land, dissolves the soluble minerals of soil and falls in rivers.
• River water contains dissolved minerals of the soil such as chlorides, sulphates, bicarbonates of Sodium, Ca, Mg, Fe.
• It also contains the organic matter (decomposed plants), small particles of sand and rock in suspension.
• Thus, river water contains considerable amounts of dissolved as wells as suspended impurities.

3. Lake Water :

• It has more constant chemical composition.
• It usually contains much lesser amounts of dissolved minerals than river water, but quantity of organic matter present in it is quite high.

4. Rain Water :

• It is the purest of all natural water. It is obtained by evaporation from surface water.
• But during journey downwards through the atmosphere, it dissolves a considerable amount of industrial gases $$(CO_{2}, SO_{2}, NO_{2}, etc.)$$ and suspended solid particles, both organic and inorganic matter .

 5. Sea Water :

• It is the impurest form of natural water. Rivers throw impurities carried by them on joining sea and continuous evaporation makes sea water richer in dissolved impurities.
• Sea water contains on an average of about $$3.5/%$$ of dissolved salts out of which about $$2.6/%$$ is NaCl.

6. Underground Water :

• A part of rain water, which reaches the surface of earth, percolates into the earth.
• As this water journeys downwards, it comes in contact with a number of mineral salts in the soil and dissolves some of them.
• Water continues its downwards journey, till it meets a hard rock, where it re-treads upwards and it may even come out in the form of spring.

 7. Spring and Well Water :

• Water is clear (due to filtration action of soil), but contains more dissolved salts.
• Thus, water is harder and has high organic purity.