With monsoon inching closer, Mumbaikars would do well to avail rainwater harvesting systems in case they haven't already. Rainwater harvesting not only helps replenish the groundwater levels, but can also help cut down on the costs incurred in buying water.
In 2007, BMC made it mandatory to install a system for rainwater harvesting on each new construction, but very few builders have implemented it. Some, in the hopes of installing cheaper alternatives, get systems that are not even sufficient to fulfill the society requirements.
Nirav Saraiya of consultancy firm NS & Associates said that many companies dupe their clients by installing a rainwater harvesting system for cheap. "This is done by reducing the size of the recharging pit (the pit from which water trickles down to the ground level); many times, they do not use the right kinds of filters. So people believe that they are doing their bit, but that doesn't even store/recharge enough for their household needs," he said.
Saraiya explains the two methods that are prevalent – rooftop rainwater harvesting and surface rainwater harvesting. For the former, water is collected in a 'First Flush Chamber', after which the water is routed to separate recharging pit with a Vee-wire filter screen kit.
The recharging pit is constructed around the bore-well, and it must be sufficiently deep to reach the underground aquifer (an underground layer of water-bearing permeable rock or unconsolidated materials) for the water to percolate.
In a more conventional set-up, the method involved using filter media of sand-gravel-stone in filtration chamber, but that led to the system being defunct in a short time due to clogging.
"It is advisable that people install a surface water harvesting system as well, to augment groundwater levels. The only additional installation in that case would be a grease-cum-desilting chamber to ensure the water going into the recharging pit is free of dirt and oil," explains Saraiya.
He estimates the minimum price for rooftop rainwater harvesting system at about Rs1 lakh and the surface rainwater harvesting at about Rs1.3 lakh. However, the cost can be recovered within 2- 5 years.
It is necessary that residents consult experts for scientifically designing a rainwater harvesting system, including a recharging pit and filter media, considering the amount of water they want to recharge and utilise.
For want of awareness and the currently cheap prices that tankers provide water at, many people do not feel need to install a rainwater harvesting system, but it is better that Mumbaikars opt for the greener option before it's too late.
