Rain Water Harvesting in India

Introduction

Now the picture is changing very fast. Rapid urbanization in India is leading us to water crisis in cities. The population exodus  will reach up to 50 % ratio till 2030. That means till 2030, 50% of our population will stay in cities and 50% in rural India. How can we fulfill their water demand both in rural & urban India? The rivers, lakes (surface water sources) are failing to meet the rising demand, therefore ground water reserves are tapped, often to unsustainable level. Many cities & villages are dependent on ground water but resulting in fast depletion of ground water table.

The major cities, are depending on rivers, lakes, tanks and open wells for water supply. The British rulers established the pipe water supply systems, around year 1870. After independence, there was gradual growth of cities. Later on it started expanding very fast. And now we are at the threshold. Rapid and unplanned urbanization, heavy water losses in existing piping systems, excess usage of water in some urban pockets, lack of strategy to augment existing water sources has pushed the cities at the brink of water crisis. The story continues in rural areas with different criteria too. In addition to quantity, we also face the problem of quality of water in many parts of the country.

India comprises of variety of climates, such as arid desert in the west like Thar, Himalayan glaciers in the North, humid tropical region in the Southwest. Many regions have different microclimates too. The Tropic of Cancer passes through middle of the country. Hence we consider the general climate as ‘tropical climate’. There are 3 major seasons considered such as summer, winter, and monsoon. About rainfall- Mawsynram gets 1187.2 cms , that is highest in India and the world , making it as wettest place on earth. On the contrary ,31.3cms in Rajasthan and overall rainfall ranges from 60 cms to 100cms. This variety in rainfall pattern makes ‘rain water harvesting’ more challenging. We get monsoon rains only in 3months-approximately 100 days, in which we get plenty of rainfall. But we have to use this water throughout the year. How we can use this water? – either by storing or using it for ground water recharge.

Rain Water Harvesting

Rain is a first source of water and rivers, lakes and wells are secondary sources of water. Rain is the ultimate source which fills all other sources. Hence  harvesting is making optimum use of rain water at the place where it falls.

Water harvesting potential = rainfall X collection efficiency.

Broadly, there are two approaches to harvest water:

1. Storing of water for direct use.

2. Recharging of ground water.

Since recharging water in the ground is more feasible and cost effective solution-more attention should be paid to this option.

Ground Water

Water in the ground is either stored in the voids of soil, rock (inter-particulate spaces) that forms the earth, which is below ground. It is like sponge, where water is stored. The rock or soil formation that holds water is known as aquifer. It is called ground water level. Sometimes it is just below the ground and sometimes it is far too deep from the surface.

Over extraction of ground water leads to gradual lowering of water level and imbalance in ground water reserves, is called depletion of water table (level). In short, depth of water level goes further down and wells become dry. You can see, this depletion of ground water in urban as well as rural areas in India. So how to refill this depleted water? It is possible through ‘rain water harvesting’.

Methods of Rain Water Collection

Rain water harvesting can be done by two methods

• Direct storage method
• Ground water recharge
• Developing ‘percolation ponds’

In direct storage method, the roof water will flow from down take pipe through sand filters. Sand filters to be installed on every down take pipe, and then water will flow to the storage tank. Though it is costly preposition we can store some water in underground water storage tank of sizable capacity which will fulfill our few days water need. The rest will flow in the ground as ground water recharge. This method is advisable where there is severe water shortage. The elements in direct storage method is storage tank of any material, sand filter, down take pipes, chambers.

Sand Filter

It is an important element in storage method. It is directly installed on down take pipe. It has first flush system , in which first two/three showers are left out and then afterwards all showers are collected in storage tank. These filters are available in the market.

Another method is using roof Water and storm water for Ground Water recharge. In that case the roof water can be filtered through sand filters but storm water needs Desilting chamber and auxiliary bore wells. The storm water can be collected through channel and gutters according to the existing topography. The physical, chemical and biological contamination can be taken care by desilting chamber. This water can be used for ground water recharge by putting it in auxiliary bore well. It will result in slow improvement of ground water table, enhancement in soil moisture and dilution of hard water in underground wells.  The problem of salinity will be reduced with this treatment. Therefore gradually the water quality will get improved. The elements of ground water recharge system are recharge pits, channels/gutters, soak away pits, infiltration trenches, oil & grit separators, desilting chambers, recharge bore wells.

Technical Details of Recharge Bore-Well

The rain water harvesting system consists of seepage / percolation pits with bore holes in the middle of the pit (4”dia) perforated UPVC pipe will be lowered in the middle of the bore holes and the pit will be filled with gravel / pebbles in two layers, each consists of boulders, gravel (1’’– 2’’dia) & coarse sand. The mouth of
the UPVC pipe shall be protected to avoid silt getting into the same. The PVC pipe of bore hole will have holes and will be wrapped with nylon cloth. This system is proposed to sustain ground water table by recharging the aquifer. The depth of the bore will depend on the soil condition / water strata. The ‘recharge pit’ will be covered by RCC slab and man-hole covers for maintenance of the pit.

Developing ‘percolation ponds’ is another important method of collection of water in the open space. Topography should be studied to locate the place of collection. With the help of small bunds, gabion walls or pitching, the water can be stored in low lying area. This method is very useful in rural areas where plenty of open space is available. In urban areas we face severe scarcity of space hence no space is available for development of ponds. If the soil is permeable then HDP sheets can be used to stop seepage, and to speed up accumulation of water. This can also be developed as ‘water body’ with good landscaping around, where entire eco-system can be flourished though different flora, fauna, bird species and aquatic life.

Conclusion

‘Rain Water Harvesting’ is a method of collecting, using and recharging available water resource in a sustainable way. It will lessen the burden on single source of water . This is rather a need of a time. Let’s join hands in the mission of ‘make every drop count’.

Name: Jyoti Panse

Mobile: 98600 99701

Email: rainharvest@gmail.com