Step 2 – What should be the RWH strategy for your layout
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Another factor to consider when determining the best RWH interventions for your context is your layout’s land use pattern. In a typical urban residential layout, land use is usually as follows: approximately 60% is rooftops, 20% is roads and the rest is open-areas like parks, playgrounds, footpaths, transformer yards or drains.
This means that the largest amount of rain is falling on rooftops. Rooftops are also clean and so rainwater running off of them is clean. It is prudent to try and capture this at the household level and use it for domestic purposes, which will reduce dependence on other water sources during the rainy seasons. It is possible in most cases to retrofit households with RWH systems, though it is worth noting to those building a new home that the cost of domestic RWH systems is significantly lower when RWH is incorporated into a new home design.
Investment in domestic RWH is done at the individual household level. The harvested water can be stored in an existing sump, in a new storage tank or for recharge. Water stored in tanks can be used for all domestic purposes, though certain precautions and treatment is necessary if it is to be used for drinking and cooking (more about this in later parts of this series). Click here for information on the components and benefits of a domestic RWH system with storage tank, and here for background on RWH using an existing sump as storage.
As for the 40% of rainfall not falling on rooftops, recharge wells are a valuable intervention to consider, as they can replenish the ground water supplying your layout’s borewells, and can also help with flood management. Recharge wells can be developed to collect run-off from common areas such as roads, parks, and storm drains. These investments will need to be made collectively. S. Vishwanath posted an informative recharge well video on YouTube.
Finally, one must consider the residents themselves and which interventions they may or may not support and why. Cost, upkeep and aesthetics are three key factors in people’s decisions to support or oppose a particular intervention.
One will usually not find the answers to these questions until they start asking.
rainwaterclub [at] gmail [dot] com
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Bangalore – 560 097
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Step 3 – Talk to an expert
Consulting someone with technical RWH expertise can further clarify the most appropriate interventions for your layout and supply you with helpful information to share with other residents. Some source of good technical input and expertise can also assist with strategising, design and implementation. This can be sourced through the market from service providers, NGOs, individuals with expertise or others who have already done it.
A note of caution: RWH design is a deceptively complex science, and it is important you make sure the expert you consult understands the fundamentals. Our advice is to confirm that your expert has experience designing and implementing RWH. Ask for their track record of successful installations.
Once you have an idea of what interventions you would like to pursue in your layout, you must enter a process of engagement with other layout residents to address various concerns and achieve clarity on all the benefits. How this process can be achieved will be covered in the Part 2 of this series.
About recharge wells and pits
1. What is a recharge pit? Is it the same as a recharge well?
A recharge pit is a hole dug in the ground. Usually it is filled with gravel or jelly to give it structural strength. A recharge well is not filled with gravel. It needs concrete rings installed in it to stabilise its walls.
2. What should be the depth of a recharge well/pit?
If you want to have effective recharge for Bangalore conditions, a 15-20 feet depth is needed. (Provided you do not hit rock before that depth). If you hit water while digging the pit, you need to ask the workers to be careful while they continue digging. The diameter of the pit you choose depends on two things: space available and the quantity of water you will send in. A 3 feet dia X 20 feet pit will ‘hold’ around 4000 litres (for recharging the ground). A 5 feet x 30 feet structure can hold 16000 litres.
3. What are the legal guidelines and their implication for recharge pit sizes?
The law states that you need to store or recharge 20 litres for for every sq.m of roof area and 10 litres for every sq.m of non-roof (ground surfaces such as parking, backyard) area. This is for plot sizes of 40×60 or more. For e.g. if your home has about 100 sq.ms of roof area, and about 50 sq.ms of non-roof area, then you will need to create capacity for at least 2500 litres of water. If you are using a 1000 litre tank to store rainwater for immediate use, you can connect the overflow to a 4000 litre (3 feet x 20 feet) recharge well.
4. How much do recharge pits cost?
Cost of digging a 3 feet diameter x 20 feet deep well is approximately Rs 20,000.
Avinash Krishnamurthy is a member of Rainwater Club.