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Global warming, climatic changes, increasing population, construction activities, industrialisation, etc. – all of these are likely to worsen the water shortage that we already face today. To deal with this problem, municipalities all over India have mandated rainwater harvesting (RWH).
However, its implementation remains inconsistent, as it is a seasonal and passive method of conserving water. At present, Chennai leads in the number of successfully implemented projects, with over five lakh installations. Cities like Ahmedabad and Delhi use purely recharging techniques. In Delhi’s Panchsheel Park Colony, for example, about 1,000 residents collected Rs 4.5 lakh to implement rainwater harvesting and in the process, have managed to save more than 170 million litres of water, annually. In Chennai and Bengaluru, rainwater from the roof is stored in sumps (underground water storage tanks) and surface run-off is used to recharge the soil. In places like Porbandar, the entire rainwater from the roof is stored in tanks.
“During the rainy season, water falls on the roofs and the ground. However, most of these surfaces (terraces and paved grounds) are hard and the water is not absorbed into the ground. As a result, most of the surface water is lost, as it flows into the drains and ends up in the sea or water ponds,” points out Sanjay Kumar Jain, a practicing architect and environmentalist, adding that rainwater harvesting (RWH) should be taken up, to solve this problem.
Benefits of RWH
RWH involves the process of diverting rainwater from surfaces to tanks or into the ground, for use at a later stage. Underground tanks can be used, to store the rainwater and it can be used for flushing or gardening. However, the amount of water that can be stored, is limited by the size of tank. Hence, an alternative method, is to dig bore-wells in the ground and divert the rainwater into it, to recharge the ground water. From bore-wells, this potable water can be pumped for daily use.
By using harvested rainwater, housing complexes and individual households can reduce their dependence on municipal water supply and/or water tankers and thereby, save money. Shaishav Dharia, regional CEO of the Lodha Group, points out that “Many developers have already installed rainwater harvesting systems in their projects. Some have also installed large Reverse Osmosis (RO) plants, to treat water from bore- wells, which would be recharged by rainwater harvesting.” Such integrated methods are necessary, to ensure availability of water, for residents, he maintains.
Different methods being adopted in urban areas
“In urban areas, this is the most popular method. In Bengaluru, this has been adopted successfully in many households,” says Shubha Ramachandran, water project manager, Rainwater Club / Biome Environmental Trust. Residents can plan the installation on the building’s terrace, courtyard or lawn of the residential complex. The simple system, uses conduits or pipes, to carry the water to the harvesting or storage area. A plot of size 12 metres by 18 metres (40 ft x 60 ft), can yield as much as 1,84,000 litres of water, in a geographical location that receives 100 cm of rain in a year.
In urban areas, rainwater falling on the ground, often flows away as surface runoff. This runoff can be collected and used for recharging aquifers, by adopting appropriate methods.
Ground water recharge
The natural water table in many areas (between 150 ft and 1,500 ft below the surface) is rapidly depleting, owing to urbanisation and the demand from an increasing population. To alleviate this situation, rainwater falling on a property, can be made to percolate into the earth, to eventually recharge the groundwater.
Things that you should check, before going in for RWH
Always hire a professional consultant, who would be able to advise you on the right design, after taking into consideration all factors, such as the topography, space and available resources. Nirav Sariya, director of NS Associates, a rainwater harvesting consultant, elaborates that “In Maharashtra, for appointment of a RWH consultant, the civic body has stipulated very specific standards for building proposal approvals.” As per the standards, one should ensure that the RWH consultant has a BE degree and is highly experienced (more than 10 years) in the RWH industry and has a proven track record, adds Sariya.
The design of the system, should be such that your investment is well-utilised. It should be economical, save space and above all, long lasting.
As it is a one-time investment, the system’s design should allow the owner to easily monitor the operating condition of the filtration pit, so that suitable precautions can be taken, if necessary. Overall, the system should involve minimal or zero maintenance.
M Shankar Rao, chief executive officer, Refurb India, informs, “The cost of a RWH system, will vary from place to place, depending on the area of your roof and the other structures that you will use to harvest rain.”
According to Mohsin Sheikh, an architect and resident of Mumbai, “The cost of a RWH structure, can range from about Rs 5,000 to drain roof water to a well, to about Rs 70,000 if it includes building a sump. For commercial installations, the cost can touch a few lakhs. However, it is a one-time investment. If implemented effectively, you may never need to pay for your drinking water anymore,” he concludes.