Chapter 8:WATER


22 March is World water day. UN recommends 50 liters of water per person per day. 2003 was the international year of freshwater observed by the UN. 2005-2015 was the international decade for action on WATER FOR LIFE.71 % of earth is covered with water.

Properties of Water

  1. Water has high boiling point, high freezing point, high heat of vaporization 
  2. high heat of fusion [controls body temperature],
  3. specific heat [leads to moderation of temperature of climate],
  4. thermal conductivity,
  5. dipole movement,
  6. excellent solvent [helps in transportation of ions in plants],
  7. Amphoteric [acts as acid and base] and high dielectric constant. This is due to extensive presence of strong bond between hydrogen.

Hardness of Water

Temporary hardness of water is due to calcium and magnesium hydrogen carbonates. It can be removed by boiling and addition of lime. This converts them to carbonates and hydroxide which are soluble.

Permanent hardness is due to presence of Magnesium and calcium chlorides and sulphates it is treated using washing soda.


Aquifers are underground water resources where water is stored between rock layers.

Earths Water Composition:


Oceans                               – 97%

Polar ice caps                       – 2%

Ground water                       – 0.61%

Lakes                                   - 0.009%

Saline lakes and inland sea     – 0.008%

soil moisture                         – 0.005%

Water vapor                          – 0.001%

rivers                                    – 0.0001%

                                                                TABLE 1: WATER SUPPLY


During rains, the canopy of trees allows water to trickle down slowly via stems and roots to theground. This ensures that water doesn’t hit ground directly as it could lead to damage to the soil by erosion.

During fires we must wrap a woolen blanket over a burning object to cut off the supply of air to it

During heavy rains, water flows into soil and covers all air pockets so earthworms rise to the surface to breathe.

Hydrogen peroxide is used as a bleaching agent, treating industrial effluents and pollution control.

Eucalyptus trees should be planted along sewage lines as these absorb wastewater and release water vapor into the atmosphere.

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