All You Need to Know About Rainwater Harvesting in Delhi

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Our team had a chat with officials at The Rain Centre, R.K. Puram and Force, the NGO that has partnered with the Delhi Jal Board to implement rain water harvesting in Delhi, to get clarity on what actually needs to be done.

For those unaware of the problem and the mandate, we request you to read through our previous blog:Introduction to Rain Water Harvesting.  Rain water Harvesting has now become mandatory for all residential houses that are 500 sq. meters and above. There are 2 rules to observe here:

  1. It is compulsory and there is no way you can shy away from implementing a Rain water Harvesting System if your house is 500 sq. Mtrs. or over.
  2. You need to construct an underground water storage tank connecting all the drains on the roof. You may construct more than one if all the drains cannot be connected to one. The formula for the storage tank is as follows:

Rooftop area (in sq meters) X 0.8 (this is the runoff coefficient. Basically it is believed that 80% of the rain water runs off and can be collected) X 0.025 (as it is believed that Delhi receives an average rainfall of .25 mm per hour).

 

This formula will give you the volume of the rain water harvesting pit in Cubic meters. This volume will be calculated from the lowest part of the inlet pipe, to the top most layer of the filter media of the ground water recharge pit. Here again, it is recommended that you build a recharge pit and not a mere storage pit, though the Delhi Jal Board doesn’t mandate the building of a recharge pit. However, it is recommended, so that the water keeps percolating into the ground and doesn’t overflow much.  The point to note here is that the Delhi Jal Board hasn’t specified any set dimensions for the pit/pits as long as the total volume of water collected is basis the above formula.

 

Delhi Jal Board Roof Top Definition for Rainwater Harvesting

A rooftop is any area that is exposed to rain, and from where water can be collected.  So, any terrace or landing exposed to rain water will be considered a roof. Currently, the Delhi Jal Board has only come out with a mandate for Roof Top Water Harvesting, so if you aren’t just looking at complying with the policy, you could also collect surface level water.

 

Rainwater Harvesting Recharge Pit Filtration

In case you plan to build a ground water recharge pit, it is suggested you add the following filter media in the specified layers so that the water percolates slowly and is purified in the process:

Layer 3: Brick Bats

Layer 2: Bajri/Gravel or Coarse Charcoal

Layer 1: Sand

 

You could also merely use Jute bags, but you would have to change them every year, as they would disintegrate. The point to note here is, that the thickness of the filter media needs to be 80 cm.

 

If you plan to build a mere Storage Tank, you would need to build a concrete floor for the tank as well. In this case, you will need to keep track of the overflow as well, during the rainy season.

 

Rainwater Harvesting Storage Tank Overflow

To manage overflows, one needs to ensure that there is an over flow pipe. This overflow pipe needs to connect to the garden in the house or an open area where the water can be absorbed. It should definitely not connect to the sewage system of the house or the mcd drains; else, it will get wasted. If you have a borewell in the house, you could also connect the overflow pipe to the borewell.

 

Delhi Rainwater Harvesting Penalty

If you decide to ignore or procrastinate implementing rain Water Harvesting in Delhi by September end, then your Delhi Jal Board Bill will increase by 50%. To avoid this penalty, you need to implement the above, and share the design of your storage tank, as well as a top view design of your entire plot, specifying the plumbing, to get clearance. This letter, along with the aforementioned designs, needs to be sent to the revenue department of the Jal Board. As soon as you send this letter, you wouldn’t be liable to pay any penalty, and can get is waived off by showing a copy of the same to the collection authority or specifying the same on the Delhi Jalboard helpline numbers.

 

Even though the penalty will be waived off as soon as the letter is sent, random checks will happen at a later date, to ensure that you have complied with the policy.

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