Updated: Feb 2019
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:
- 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.
- 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. A simple prefilter (jail) is a good idea on all the inlets on your roof/terrace in order to keep leaves and other material from choking your pipes. A simple pre-filter (jail) is a good idea on all the inlets on your roof/terrace in order to keep leaves and other material from choking your pipes.
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.
Rainwater Harvesting Cost
Based on data from a couple of implementations we have seen personally, as well as discovered online the cost of setting up rainwater harvesting for a 500sqm plot is about Rs. 1L. This includes the cost of building the tank with filtration mentioned above, setting up the piping to channel rainwater into the tank, and creating a mechanism to use the water in the tank (assuming you are collecting and using the water instead of recharging the ground water).
Delhi Rainwater Harvesting Penalty
If you decide to ignore or procrastinate implementing rain Water Harvesting in Delhi, then your Delhi Jal Board Bill will increase by 50%. On the other hand those who do implement rain water harvesting will get a 10% rebate on their bill, thereby making the delta for not conforming to rain water harvesting almost 66%. 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.