Water on the earth is being recycled continuously in a process known as hydro logic cycle. The hydro logic cycle begins with the evaporation of water from the surface of the ocean. As moist air is lifted, it cools and water vapour condenses to from clouds.Moisture is transported around the globe until it returns to the surface as precipitation. Once the water reaches the ground, one of two process may occur; (i) some of the water may evaporate. back into the atmosphere or (ii) the water may penetrate the surfaces and become grounding water. Groundwater either seeps its way into the oceans, rivers and streams or is released back into the atmosphere through transpiration of plants. Groundwater is the major source of water for many cities. But as the population increases and the need for water also increases , the ground water level in some areas is getting dangerously low. Added to this problem is an increasing amount of population that seeps into groundwater. In the future with growing anthropocentric activities and more toxic wastes the hydro logic cycle we depend on become dangerously imbalanced. 21. The word `transpiration' mean-