Rain water harvesting has been in the talks recently for saving the rain water underground. This is vain talk; rain water will not stay underground. One can see well water swell from 70-80 feet deep to the brim during heavy rain but soon after the rain stops it recedes back to the pre-rain level within ten or fifteen days. Where does the water go? You can see where the surface water goes during incessant rain – yes, it flows into the sea; similarly, rain water that is directed underground will eventually reach the sea flowing and moving underground towards the sea. The sand near and close to the shore can be dug to 5′ to 10′ deep and you would find there such sweet potable water; it will never be salty and bitter . It is not the sea water creeping into the land area; but on the other hand it is the water from the land flowing into the sea from the underground water table. You can never harvest rain water for it would by nature’s law flow into the sea.
In the near-by area of the down-stream of dam water, we can easily pump out the ground water from a relatively superficial depth compared to the area in the upstream. As one proceeds farther and farther away from the dam water storage the water recedes to deeper and deeper levels. You can never harvest the rain water.
The water table goes down during the hot sunny days; this is because we can see the water from the deepest depths of the ground pulled up to the surface of the earth from where we can see the water evaporating even from far off distance. The amount of evaporation is so heavy that the mirages are visible in the heavy waters of evaporation. You have to stop this to increase, retain and to create the underground water table. You can never harvest the rain water.
While during the day time the underground water evaporates, the reverse of it happens during the nights as the water cools above the surface of the earth. The trees with their shades protect the ground water in the day time from evaporating and breeds the ground water during the night chill. This is the only way by which the ground water is created and definitely not through rain harvesting. You can never harvest the rain water. It would recede into its down stream; either it reaches the sea or dries up in the land somewhere far away in the land.