With growing population, finite natural resources are decreasing. There is continuous increase in demand of portable water supply for Hyderabad. Water is no longer abundant resource. With short fall in supply of potable water, there is continuous over exploitation of ground water of ground water to bridge gap between demand & supply. At some places, the ground water is at more than 50meter deep below ground level. Therefore, it is essential to arrest this situation and to enhance ground water potential for Hyderabad.

Rain Water Harvesting is collection and storage of rain water that runs off from catchments areas like roofs, pavements, roads parks, open ground etc. this rain water can be collected and stored as surface storage in tanks or can be recharged into the ground water.

Surface storage of rain water is a traditional technique and structures used are surface tanks, underground tanks, ponds, lakes, check dams etc.

Artificial Recharge of ground water is relatively new concept of harvesting rain water. Rain water falling on roof tops and other areas and where sufficient space is not available for surface storage is guided into sub-soil water through various techniques. Structures generally used for this purpose are:

• 1. Recharge pits
• 2. Recharge trenches
• 3. Recharge Shafts
• 4. Trench with Recharge Bore Well
• 5. Recharge through existing dug well
• 6. Recharge though abandoned tube well, abandoned hand pumps
• 7. Percolation tanks etc.

People planning construction of House, Modification of house, existing house, etc. from rooftops
Govt. Buildings, Institutions, Hospitals, Hotels, Shopping malls etc. from rooftops and open areas Farmlands, Public Parks, Playground, etc.
Paved and unpaved areas of a layout / city / town / village

You, me and everybody! It will not only provide you with water in times of acute water shortage, but will also recharge the groundwater and increase its level.

No, existing buildings can also implement RWH by modifying the existing plumbing and making additions, if necessary.

The cost will vary depending upon the catchment area and the conveyance/ storage structures finalised. RWH can be installed at a very low cost in large plots where public buildings, schools & colleges are located, and this cost is negligible to the total construction cost, if integrated with the building design.

If planned in an existing building, the cost is higher due to extra plumbing involved, but the returns are rich in terms of recurring benefits. 

Can the stored rainwater in storage tanks be used for cooking and drinking?

The rainwater that falls on the roof is pure, but since it comes in contact with various surfaces on its way to the storage units, some dust and leaves may get carried away with it. This can be reduced if the terrace is swept before the rains. However, even if some dust or leaves go into the sump, they do not cause any harm as long as the water is boiled before consumption.

Various filters can be utilised to remove such suspended pollutants from the rainwater collected to make it safer for consumption.

A concrete, tiled and paved area of 100m. Sq. size yields about 56 thousand liters of rain water annually (for Hyderabad) for recharging of ground water. Even if it is considered that 75% of it can be harvested effectively, the volume of water harvested would e about 40 thousand liters. This volume is about seven times the annual drinking requirement of a five-member family. The minimum drinking water requirement per person is 5 liters per day (IS 1172/1983)

The RWH system must ensure that not a drop of rainwater falling within the premises is let into the sewerage or wasted as runoff. This can be achieved only if the method adopted within the premises satisfies the following criteria:

• Completeness: Both rooftop and driveway runoff water must be harvested.
• Apportioning of water: To avoid overload of any one system, leading to overflow and loss.
• Proper design: Volume of water likely to flow through and the nature of the soil in the area should be considered.
• Maintainability: Design should incorporate features allowing for periodic maintenance of the structure.

Existing unused structures like dried open wells, sumps etc can be used for RWH as also defunct borewells, instead of constructing recharge structures. This will also reduce the total cost.

It is a process by which the groundwater is augmented at a rate exceeding that obtained under natural conditions of replenishment. Any man made scheme or facility that adds water to an aquifer may be considered to be an artificial recharge system.

Gravity based rain water harvesting system for direct recharge of ground aquifers generally consists of filtration cum recharge chambers/ trenches and recharge bore-well. De-silting chambers may be provided in case of heavy silts are carried by rain water.

For general guidelines, recharge chambers are designed for a capacity of 2 cubic meters (2000 liters) of 100 square meter of roof top area/concrete paved area. Recharge chambers normally have 3 layers of filter media. For larger size catchment areas recharge units are to be suitably designed. A recharge bore of 100mm nominal diameter is provided to carry filtered rain water directly into aquifer zones, where post monsoon depths of ground water levels are more than 15m. Depth and size of recharge bore is dependent on porosity, hydraulic conductively, natural recharge water balance, litho logy and depth of the aquifer.

Central Ground Water Board has provided General Standard designs for rain water harvesting on their websites for public facilitation.

Abandoned tube-wells can be used for recharge purpose. However, it need to be cleaned and developed to clear any clogging of slots. Before utilizing the abandoned tube wells as recharge structures. It is to be ensured that they are taking water. Slug test may be conducted to obtain preliminary information on aquifer parameters for suitable designs of recharges structures.

It is essential that the rain water harvesting systems and its components once constructed are maintained in proper why for their effective utilization. Some of the precautions that should be taken are:

• 1. Implement the rain water harvesting scheme in proper way, adopt the system/method which is most efficient and economical as per site conditions. The solution to any water harvesting problem is site specific.
• 2. Install rain water harvesting structure at the construction stage itself as it is more economical and easy that installing in an old building or house.
• 3. In general, harvesting rain water in areas where the ground water level is at a depth of more than 5.00 M below ground level.
• 4. Entry of highly turbid water into recharge well should be prevented
• 5. Keep the roof and catchments area clean so as to harvest clean rain water.
• 6. It is preferable to have silt chamber before the recharge structure to trap the silt.
• 7. Provide mesh filters at the mouth of drain pipes to exclude the debris.
• 8. Domestic waste water, sewage water and contaminated water should not be allowed for recharging.
• 9. For harvesting rain water of storm water drains, it is essential that they carry only the rain water and there is no inter mixing of waste water.
• 10. Do not store any chemicals, oils, paints, lubricant or fertilizers on the catchments areas.
• 11. Periodical maintenance for recharge structures to be carried out.

Recharge of ground water through rain water is long continuous process. It is sort of investment for our younger generation to come. In addition to recharge of ground water, rain water harvesting benefits in many ways like:

• 1. Improves quality of ground water.
• 2. Reduces soil erosion as the surface runoff is reduced.
• 3. Chocking of drains is avoided thereby flooding on road during monsoon can be minimized.
• 4. Saving of energy, one meter rise in ground water level saves about 0.4 KWH of electricity.

RWH can be traced back to thousands of years in India. Our ancestors traditionally harvested rainwater through tankas, johads, madakas and many such local innovative structures that can be seen even today, across the country.

3 steps to begin RWH:

Step 1:  Ask yourself: Why Rainwater Harvesting? Your answers to the questions below will help determine the most appropriate RWH interventions. In many cases RWH is implemented to achieve all three of these objectives. 

• 1. Is it a source of supplemental water (thus reducing demand from your existing sources)?
• 2. Is it to recharge ground water sources as you are dependent on borewells/open wells?
• 3. Is it also as a flood control measure?

Step 2:  Understand the strategy for your layout.

• 1. Consider the land use pattern
• 2. Choose domestic RWH system with storage tank or use an existing sump as storage
• 3. Need for investing in recharge wells
• 4. Engagement with people, discussion with other residents as water managers

Step 3:  Talk to an expert