Rain Water Harvesting

Introduction:
“The consumption of fresh water around the world has risen by six folds from 1900 to 1995. This rate is twice the rate of population growth during this period. Already, about ⅓ of the world’s population lives in “Water Stressed” countries where consumption exceeds 10% of the supply. If this trend continues, two out of three people will live in the condition said above by 2005”…. This is the statistics revealed by none other than Mr. Kofi Annan, the UN Secy. General.

Water was so easily available that it was abused rather used in all these years and hence has become the most precious resource. It is not an exaggerated statement if some one said that “Water would be the major bone of contention in a probable World War III”. Large variation in the availability of potable water and growing demand has mooted the need for rain water harvesting.

Why harvest only rain water?
Rain water is the primary source of pure water available in the earth. Even if we recover a small portion of the rain water that is wasted into sea, we will be provided with a new precious resource.

Around the world, only about 23% of the rainfall is received on land and the balance in oceans. Only 2.5% of the water available on earth is fresh i.e. 35000 Km³. Out of this, 69% (25000 Km³) of them are present in non-usable forms such as icecaps, glaciers, moisture in air, soil etc.,. The remaining fresh water is available as ground water.

India has got around 7000km long coastal line. Overdraw of water from ground along the coastal areas had led to intrusion of saline water from the sea. The above problem is observed in areas of TamilNadu, Saurashtra, Andhra Pradesh, and West Bengal. One should realize that even less than 2% of the sea water can spoil the water potability. Though variety of methods is recommended for remedies, artificial recharge or rainwater harvest is the easier and cost-effective method to prevent this.

Rapid urbanization and industrialization had increased the demand for fresh water and thus depleting substantially the ground water table. Secondary sources like rivers, lakes are either vanishing or contaminated. In India, the average rainfall is 1170mm which is relatively high against the global average of 800mm. Poor storage facilities in the catchment regions and wastage of rain water being allowed to flow into sea add to the problems. Under these circumstances, rain water harvesting alone can revive the hope of recharging the ground water to maintain the sustenance of the planet.

Catchment Area:
The direct surface area that receives rainfall and contributes to rain water harvesting system is called catchment area. This could be the paved area on the terrace of a building, unpaved areas like lawn or open ground, sloped sheets of asbestos or PVC. The water collected in these areas can be conveyed to storage area vide PVC, HDPE or GI pipes. Plastic pipes are preferred as GI will react with the rain water which is soft in nature and produce ferrous oxide.

Re-charge by Percolation pits:
A sump needs to be built according to the rainfall amount and the catchment area. If the terrace is about 14000m² and the average rainfall is 470mm per month, (Chennai) then you can construct a sump of 50m³ (5x5x2). Do not plaster this. This sump should be dug near the bore-well pipe or well.

Fill the sump with river sand. Then fill with gravel, pebbles (coarse / big), smaller pebbles with coarse sand, coal mixed with broken brick pieces and fine sand. All of these should be filled layer after layer inside the RCC rings in equal amount. The RCC rings should have holes for aeration. Now bring the catchments pipes from the terrace (keep a gradient of 1:100 1cm slopes for every 100cm for natural faster flow) and drop the pipe on these layers. Cover the sump with a hole for aeration. The water collected will be filtered through or percolated through and get collected at the bottom. This collected water will re-charge the ground water table and dilute the hardness of the same.

Some ask what Acid rain is. How to harvest it? Water is neutral in normal state. Whenever the pH value goes below 7 it becomes acidic and goes beyond 8.5 it becomes basic. It literally does not mean that acid is raining as said. Cochin, Chembur, Kalyan, Delhi, Dayalbagh, Korba are some sites where acid rain fall takes place. Due to air-pollution, the pH value of rain water is getting lower in all major cities in India. This is a matter of concern.

Re-cycle of Sullage:
The sewage water can be treated and re-cycled at a cost of Rs 35/- per sq ft with a basic land cost at Rs 2000/-. The bath water and wash water in households known as sullage could be treated and re-used for low-end purposes like vehicle cleaning, gardening, floor-washing and to re-charge ground water. In houses with mini RO plant, the discharge water can be used for utensil washing. Preventing the use of potable water for non-potable purpose should be imbibed among us. This means use of drinking water for washing clothes or bathing should be stopped.

Conclusion:
Governments after Governments had promised fresh drinking water to every individual but it all remained as a dream that would never come true. We, on our part also are to be blamed as we always expected others to do something for us. It is the high time that we started conserving the precious resource – water. Unless the imbalance between ground water depletion and water recharging is rectified, more dangerous situations are in store for us in years to come. As the sons of the soil, it is our responsibility to collect rain water, utilize it judiciously and return to Mother Earth for sustainability.