Rain Harvesting

Rainwater harvesting (RWH) is the collection and storage of rain, rather than allowing it to run off. Rainwater is collected from a roof-like surface and redirected to a tank, cistern, deep pit (well, shaft, or borehole), aquifer, or a reservoir with percolation, so that it seeps down and restores the ground water.

What is the rainwater harvesting process?

The process of rainwater harvesting involves the collection and the storage of rainwater with the help of artificially designed systems that run off naturally or man-made catchment areas like- the rooftop, compounds, rock surface, hill slopes, artificially repaired impervious or semi-pervious land surface.

Why rain water harvesting is important?
Rainwater harvesting helps utilities reduce peak demands during summer months, saving treated water for more important and appropriate water uses. While rainwater can be a perfect primary water source for many uses and situations, it is also a great backup water supply for emergency situations

Is rain water harvesting worth it?
Economic Benefits

Low Water Treatment Cost: Rainwater harvesting reduces the energy cost involved in pumping and treating water by the municipalities for the residential buildings.
Lower Water Bills: Rainwater harvesting is an excellent alternative to municipal water, and it reduces your water bills

What are the uses of rainwater?
Here are some uses of rainwater:

  • Drinking water if properly filtered and sanitized.
  • Irrigation or sprinkler system.
  • Laundry.
  • Washing of vehicles.
  • Washing of garage or sidewalks.
  • Cleaning of toilets.
  • Swimming pool refills.
  • Fountain or fishpond refills.


Tannins in drinking water are caused by natural decaying of organic matter. Leaves or pine needles in the gutters are generally the cause in a rainwater collection system. A faint yellowing of water generally occurs at .5 parts per million or PPMs with .5 – 2.0 PPMs looking like the color of ginger ale, and 3.0 – 5.0 PPMs would take on the appearance of dark tea. The tannins may cause a yellow color of the water, yellow staining on fixtures, and yellow staining in laundry.

Although aesthetically displeasing, tannins generally pose no real health risk, but may affect the performance of the UV system by not allowing the UV light to penetrate thoroughly through the water column.

Therefore, it is very important to minimize tannins before storage of collected rainwater. Organic matter must be kept from accumulating in gutters, down spouts, and screen baskets. Gutter screens are an effective method of prevention of organics in gutters and down spouts. Both gutter screens and screen baskets should be inspected and cleaned as needed to prevent tannins from occurring. Since the discoloration is in solution, removal can be difficult and expensive. Ozone, ion exchange, and activated carbon can help with removal of tannins to some degree. If you do end up with tannins in your water, it is best to drain the cisterns, rinse and start collection again, however the best solution is diligence in maintenance.

What are the disadvantages of Rainwater Harvesting ?

Unpredictable Rainfall: All places do not receive the same amount of rainfall. It is also difficult to predict rainfall. Therefore it is not advisable to depend on rainwater alone for all your water needs in areas where there is limited rainfall. Depending on rainwater harvesting alone, is suitable in those areas that receive plenty of rainfall.
Initial High Cost: It is not possible to predict the cost recovery period of a rainwater harvesting system. Also the initial installation cost for the same may increase depending on the system’s size and technology level.
Regular Maintenance: Rainwater harvesting systems are prone to rodents, mosquitoes, algae growth, insects and lizards which contaminate the harvested rainwater. They can become as breeding grounds for many animals if they are not properly maintained.
Certain Roof Types may Seep Chemicals or Animal Droppings: Certain types of roofs may seep chemicals, insects, dirt or animals droppings that can harm plants if it is used for watering the plants.
Storage Limits: One of the biggest disadvantage of rainwater harvesting is the storage facility. It is restricted not only by the size but also by time.

What government is doing for rainwater harvesting?
The state Roads and Buildings Department has made rainwater harvesting mandatory for all government buildings. Haryana Urban Development Authority (HUDA) has made rainwater harvesting mandatory in all new buildings irrespective of roof area. The CGWA has also banned drilling of tubewells in notified areas.

                                          Laws and Policy


The Central Ground Water Authority (CGWA) has directed Group Housing Societies/Institutions/Schools/Hotels/Industrial establishments/Farm Houses in South and South West Districts and group housing societies located outside notified areas of NCT of Delhi where ground water levels are more than 8 meters below the ground surface to adopt Roof Top Rain Water Harvesting systems in their premises.

Ministry of Urban Development and Poverty Alleviation, Govt. of India has made modifications to the building bye laws that requires Water Harvesting through storing of water runoff including rain water in all new buildings on plots of 100 sq. meters and above will be mandatory.

Building plans are not sanctioned unless such provision is provided. DDA/MCD representatives undertake a site inspection before issue of Completion Certificate to the building and ensure that the RWH is made as per plan.

Buildings with plots of 200 sq. meters or above that extract ground water through tube wells, bore wells, etc need to implement Rain water harvesting.

Financial assistance is given to a maximum of 50% of total cost of the Rain Water Harvesting structure or Rs. 1,00,000 whichever is less. Contact RWH Cell for more info.

Rainwater harvesting has been made mandatory in all new buildings with an area of 500 sq meters or more.


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