Mumbai: Water conservationist pushes for rainwater harvesting percolation pits

A water conservationist has devised a plan to kill two birds with one stone He has come up with a solution to address two issuesmdashtoo much water in monsoon and too little water under the groundTo reduce waterlogging during the monsoon and recharge depleting groundwater level Subhajit Mukherjee is giving away 2500 barrels for installation of rainwater harvesting percolation pits at housing societies So far 1500 barrels have already been distributedThrough his organisation Mission Green Mumbai he has stepped up efforts to popularise the rainwater harvesting concept in the city as May and June are considered critical months for installing the systemHe also trains and gives a demo of the installation at Rajiv Gandhi Udyan in Kandivli WestMukherjee said ldquoWhen you give it for free people are curious and want to learn more about it They become interested in learning People also seemed to have appreciated my lowcost method Typically a rainwater harvesting system costs around R1 lakh My formula costs less than R1000rdquo he saidThe city receives 3750 million litres per day MLD of water from the civic body whereas it requires 4200 MLD To reduce dependency on reservoirs the BMC in 2002 mandated that all new constructions larger than 1000 square metres install rainwater harvesting systems in order to obtain an occupancy certificate OC Later plots larger than 500 square metres were also asked to include rainwater harvesting unitsldquoMany societies have the system in place but not all of them maintain it We are focusing on encouraging societies to adopt rainwater harvesting as soon as possiblerdquo said a senior civic officialldquoThe big gamechanger for Mumbai in terms of improving water supply will be treating sewage water We are working feverishly on it Simultaneously rainwater harvesting method utilising percolation pits will help recharge the groundwater table while also reducing waterloggingrdquo the official addedHow the system worksThe rainwater percolation pit is a simple mechanism wherein a pit is built to collect rainwater which then slowly percolates into the soil It channels rainwater from your terrace into a specially designed underground pit to conserve and recharge groundwater as well as ponds lakes bore wells deep tube wells etcThe method entails digging a 10x10 feet pit and filling it with pebbles and stones The chamber also has a channel for collecting water which eventually recharges the groundwater ldquoThere is an estimate that a 6x6 feet pit helps to take 1000 litres of water into the landrdquo Mukherjee saidWhy the needDue to rapid concretisation Mumbai is flooded every monsoon According to research there is over 70 per cent increase in concrete surfaces in the city reducing absorption of rainwater leading to depletion in groundwater levels ldquoTrees do not survive and the frequency of heat wave is rising because of depleting groundwater levelsrdquo Mukherjee pointed outMoreover it is causing health problems increasing surplus heat and decreasing oxygen levels he saidHe added ldquoSo far over 5000 people have attended the demo for installation However not all societies have space for percolation pits We are giving away barrels to societies that have spacerdquo2500No of barrels being distributed for free