Rainwater Harvesting

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Rains are a major source of water for us, many rivers feed out of it. However, much of the water goes waste when we allow it to run off and enter urban drains. Hence it is extremely important to accumulate, the water through roof drains, into underground reservoirs, for use.

Rainwater can be used in gardens, in toilets, and for domestic use with proper treatment. The harvested water can also be used for storage and for other purposes such as groundwater recharge.

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Suitable for roof top area upto 100 sq.metres  

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 Abandoned/ Running Hand Pump 
Suitable for roof top area upto 150 sq.metres

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Abandoned Dug Well 
Suitable for roof top area more than 1000sq.metres 

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Recharge Trench 
Suitable for roof top area — 200 to 300 sq.metres

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Gravity Head Recharge Well 
Suitable for roof top area more than 400sq.metres 

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Recharge Shaft 
Suitable for roof top area greater than 1500 sq.metres

 All images sourced from: Delhi Jal Board

Why Should we Harvest Rainwater?

With rapid urbanisation and the growth in population, the existing portable water supply is no longer sufficient to meet consumption needs.  According to the Delhi Jal Board, based on its present population, Delhi’s water requirement is 800 MGD (million gallons per day), while the total water supply from all sources is 670 MGD. Delhi gets most of its water from neighbouring basin states like Haryana, Himachal Pradesh, and Uttar Pradesh etc. Thus, the Delhi Govt. is limited in augmenting its water supply, leading to increased pressure on ground water.

With the receding water table, it has become all the more imperative to adopt Rainwater harvesting techniques.

Rainfall usually occurs in high intensity short spells, resulting in a run off, rather than recharging the ground water levels. Rainwater harvesting helps chanelise this runoff water, and store it. Rainwater is bacteriologically pure, free from organic matter and soft in nature. Moreover, it can be used to recharge the ground water levels  . Another advantage of rainwater harvesting is to reduce the . In fact, rainwater harvesting systems have been put in place in Chennai, and the Delhi Government has taken inspiration from them.

According to rainwaterharvesting.org:

Potential of rooftop water availability in National Capital Territory of Delhi

Roof Area in Sq.m Annual rainfall in (litres) Quantity of rainfall available for harvesting (litres)
50 30,550 18,330
100 61,100 36,660
500 305,500 183,300
1000 610,000 366,600

(Note: a.Annual average rainfall of Delhi=611 mm; b. runoff coefficient is assumed as 0.60;Sq. m to be read as square metre)
An analysis done based on the rainfall availability and demand supply gap shows that even 50 per cent of the rainwater harvested could help in bridging the demand supply gap.

What is the state of the Ground Water Table in Delhi?

According to an article in the Hindu, dated August 2014, the state of Ground water is dismal, especially in south and south-west Delhi. Here are some facts and figures from the article, to give you and idea.

What is the Delhi Jal Board mandate, what have they asked homes to do?

Considering the gap in supply and demand of water, and the ground water levels in some areas, the Delhi Jal Board has made it mandatory for all existing residential with an area of 500sq m and above, to install rainwater harvesting systems. There are around 10 areas where groundwater levels are reasonably high. Vetted by the Central Ground Water Authority , these areas will not be required to carry out RWH. These include Okhla, Siddharth Extension and Jahangirpuri.*

If you’re looking to implement rain water harvesting in your Delhi home, BuildingBlox can help. Please fill the BuildingBlox Rainwater Harvesting Form and we will contact you.

*For  more details on the Rain Water Harvesting Mandate, do lookup the Delhi Jal Board website https://djb.gov.in