Dangers of improper rain water harvesting

Nainital Lake

Over the last century, human population has grown and along with it there has been a tremendous growth in cities. A direct consequence of this growth is that urban populations in many cities across the world are facing water shortages. Along with sunshine and fresh air, water is a primary requirement for life and any shortage in its supply spells a diminished quality of life.

There are primarily three sources of water available to human populations – rain, surface water such as lakes and rivers and lastly ground water. The source of all three is rain that rises from the abundant oceans on the planet. However with increasing use and population growth, both surface and ground water is not only getting depleted but also getting polluted.

Whenever water shortages occur there is often a cry to conserve water. One basic point is forgotten in this cry – WATER CANNOT BE DESTROYED – by most natural processes. It requires chemical and other possesses such as electrolysis to destroy. In most cases water is recycled over and over, therefore cities facing water shortages need to reexamine the recycling processes that are taking place in the city.

A solution that has been proposed in some cities is called Rain Water Harvesting. It is suggested that rainwater should be collected and directed to deep bores inside the ground so that it reaches underground sources. A primary shortcoming of this process has been overlooked. When surface water percolates naturally to underground sources it undergoes purification through natural filtration. If it is directly sent into the ground to the water table or close to it then surface pollution reaches the ground water without the benefit of this purification. The result is that ground water is then polluted and loses its potable quality.

The alternative of directing rain water to shallow covered pits (of no more than ten feet depth ) is safe since then an adequate ground depth may still be available for purification. However such pits, although good for daily domestic waste water are usually not enough to store rain water.

In case a city desires to increase its ground water supply the alternative of storing rain water in several artificial lakes in and around a city or town is a viable option. In this case the water purifies as it percolates into the ground. It can then be pumped out to augment city supplies with minimal treatment. Further the city waste and sewage water too can be treated in a similar manner by directing it into lagoons designed to purify the water through both aerobic and anaerobic processes. Eventually some of this water percolates into the ground to improve ground water supplies. Such systems exist in several towns around the world. These lakes need to be stocked with fish in order to minimize the menace of mosquitoes. Usually, such lakes need to be aerated otherwise the depletion of oxygen in water causes the fish to die from time to time. Wind Mill driven or solar cell aeration systems are a better option than electricity driven pumps. Solar and wind devices produce intermittent electricity or intermittent mechanical power and that is what is precisely required by lakes for aeration.

Surface storage of water is therefore the proper way to store rainwater whereas the so-called Rainwater Harvesting that directs water deep inside the ground is the improper way. One need not worry about the loss of surface water through evaporation from lakes and ponds in large countries bounded by mountains as in India since that tends to augment precipitation and return to ground again as highly pure water in the form of rain. Dams serve the same purpose as surface lakes but whereas large dams may have an adverse environmental impact, small dams and lakes improve the environment.