Part 1 and Part 2 of our series on rainwater harvesting (RWH) exposed how the government as well as citizens have failed in making the most of a scheme that, if implemented well, could have set Chennai as a worthy example in water management.

While negligence on the part of authorities has been a crucial factor, lack of awareness on RWH as a whole also plays a major role. There is a need to dispel the ignorance or misconceptions among residents, many of whom feel that the construction of RWH structures cost a bomb.  

Experts who have worked on rainwater harvesting will tell you that the model has both monetary and environmental benefits. “While a lot of the monthly water budget can be cut down drastically, you can also feel good about the fact that you are saving the precious resource for generations to come,” said  hydro-geologist J Saravanan.

So, if you are wondering how to go about this, here’s a round-up of the basic steps.

Know the rules and regulations

If your building has more than six dwelling units and three floors, Chennai Metropolitan Development Authority (CMDA) is the relevant monitoring authority. A building completion certificate is provided only if it has a RWH structure.

In buildings with less than six dwelling units, engineers from the Chennai Corporation are the authorized officials for inspection. The Chennai Metro Water department, which does a final check, will provide water and sewer connections only if the building is equipped with RWH infrastructure.

How to harvest rainwater

It is crucial to harvest both the rooftop and the setback areas in a household, to preserve precious drops of water from getting into the sea. Roof-top rainwater harvesting (RRH), which can be implemented in individual houses and apartment complexes, involves diverting and storing a part of the rainwater that falls on the roof of a house.

The stored water can be collected into a recharge pit, which reaches the soil and recharges the aquifer. Water can also be directly collected into sumps; this option is particularly feasible for those areas in Chennai with no supply from Metro Water.

While it is true that the municipalities have provided overhead tanks in some areas to meet the additional water demand, it is not an easy or convenient option for many to walk to those areas, stand in a queue and collect water. Collecting rainwater in the sumps could help meet the water needs of a suburban household and reduce their monthly water budget, which typically goes beyond Rs 2000, for a family of three.  

The method

Harvesting rooftop water is simple; all you need is a clean terrace, a downward pipe connecting the roof and the recharge pit, and a rainy filter to screen the dust particles. An underground storage tank is necessary, if you are not recharging the aquifers.

To retrofit your house with RWH infrastructure, connect the terrace with a pipeline. The first flush water collected from the rooftop would be filled with concentrated dust and charcoal. A rainy filter is necessary to get rid of them. Thus, engineers would place a rainy filter at the downward moving pipeline which filters the dust particles.

M Jesudasan, Managing Director of J L S Traders, a RWH company explains, “Functioning of the rainy filter needs no electricity. Water is pushed through the filters by the centrifugal or gravitational force. The 90 percent pure water with minimal presence of dust can be diverted to open or closed wells.”  

This process could be employed in residential as well as commercial complexes. On average, water from a 1000 square feet terrace can be sent to a borewell of 60 feet depth. The procedure for a 1000 – 1200 square feet household would cost around Rs 5000 – Rs 8000 (to fit the pipelines and insert the rainy filter)

In the absence of a borewell, water can be sent into the soil by digging a pit to a minimum of 10 feet to 20 feet, depending on the soil type in your locality.

To harvest the runoff water, a sump should be constructed in front of the entrance, as enabled by the space available. This costs anything between Rs 5000 to Rs 12,000, depending on the capacity. The sump should be connected to the overhead tank.

It may be noted that the soil would be deposited in the sump, providing clean water to the households.  

A detailed account of how rooftop water harvesting can be done efficiently can be found here.

Setback harvesting, a must

Many households have confined themselves to rooftop harvesting alone, overlooking the fact that a lot of water from the setback area is let into the drain. By harvesting the water from the setback area which typically includes the driveway, balcony, garden and front yard, the burden on the city’s clogged stormwater drains can be  reduced.   

A recharge well at the entrance of every household would conserve the runoff water, besides preventing water stagnation on the streets. If one looks at the current state of the stormwater drainage system of Chennai city, most of these drains will be found to serve as sewage water carriers, filled with plastic and household waste. Even where the drains are clean, a majority of them are not connected to aquifers. So, a citizens’ efforts to have a comprehensive RWH structure at their residences can be a blessing.

Caveat

Do not use pebble stones as the filtration medium, as they need to be cleared of the silt regularly. Soil, as a natural filter, does the job.

It is also very important to understand the different soil types that the city has. In an earlier article in the series, experts had shared how rain water should be harvested after considering the soil type in the particular area.

Knowledge resources

If you are looking for some additional information or technical assistance before you embark on installing a rainwater harvesting system in your house, you may consider consulting any one of the following experts:

Sekhar Raghavan, The Rain Centre: +91 9677043869

M Jesudasan, J L S Traders: +91 7418294967

J Saravanan, water expert: +91 7299983696

Indukanth S Ragade, rainwater harvesting expert: +91 44 28153506