Updated Feb 2019
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.
Suitable for roof top area upto 100 sq.metres
Abandoned/ Running Hand Pump
Suitable for roof top area upto 150 sq.metres
Abandoned Dug Well
Suitable for roof top area more than 1000sq.metres
Suitable for roof top area — 200 to 300 sq.metres
Gravity Head Recharge Well
Suitable for roof top area more than 400sq.metres
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)|
(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?
A graphic published in the Times of India in May 2018 showed the following figures:
|Neighborhood||Depth to water level(m)|
A previous article in the Hindu dated August 2014, suggested 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.
|Region||Depth to water level(m)||Area in sqkm|
|Central, North-West, North||0-2||3.8|
|New Delhi, East, South-West, North-West||5-10||287|
|South West, New Delhi||10-20||410|
|South-West, South, New Delhi||20-40||247|
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.*
What effort does it take to Maintain a Rain Water Harvesting System?
Estimates suggest the cost of maintaining your rainwater harvesting setup could be of the order of Rs. 5k per year. You should get your tank cleaned 1-2 times a year based on the rainfall season in your region. Also make sure the inlets are not blocked with waste which could impede the flow of water. You could also use alum in the water to help the dust settle down to the bottom in order to make the water clearer for use, however ensure that you don’t use the water for cooking or drinking in that case.
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