Mumbai could save water through its mandatory rainwater harvesting rule – but no one seems to care

Sumesh Lekhi’s housing society in Mumbai’s Versova suburb decided to install rainwater harvesting facilities in their colony as far back as 2001. They planned to collect rainwater during the monsoon months and use the stored water for things like flushing toilets and washing cars, so that they could reduce their dependence on the municipal water.

The Municipal Corporation of Greater Mumbai sources water from seven reservoirs. The water levels fluctuate with the rains.

To reduce the dependence on the reservoirs, in 2002, the municipal corporation made rainwater harvesting mandatory for all new building constructions in Mumbai covering more than 1,000 square metres. In 2007, the rule was made even more stringent: all new constructions covering more than 300 square metres were required to have in-built rainwater harvesting facilities, without which buildings would not be given occupational certificates.

The rule aimed to ensure that buildings would store enough water during the monsoon for non-essential purposes for the rest of the year.

But in the 17 years since the rule came into force, rainwater harvesting has been poorly implemented across Mumbai.

There is no clear data available on how many new building constructions have rainwater harvesting facilities. But if most residents went looking around in their own neighbourhoods, they would be hard pressed to find one. In the buildings that do have the infrastructure to harvest rainwater, the stored water often goes unused.

Take Lekhi’s housing society, for instance. The building is located in a suburb along the western coast of Mumbai. A few years after the rainwater harvesting facilities were installed, residents found that the stored water was turning saline and brackish.

“The water was corroding building pipelines and causing cars to rust, so people stopped using that water,” said Lekhi, a citizen activist who has observed several other buildings in his neighbourhood facing the same problem. “In another nearby area, I know of buildings that stopped using harvested rainwater because it was getting contaminated by waste water from a slum nearby.”

Depleting water resources

Every day, residents of Mumbai consume more than 3,500 million litres of water, supplied by reservoirs located to the north of the city. In November 2018, when water levels in all the reservoirs dropped to 75% of their total holding capacity, the Municipal Corporation of Greater Mumbai announced 10% water cuts for the whole city.

The monsoon in 2018 had not been good enough to fill up the lakes, and the corporation hoped that a relatively small water cut for eight months leading up to the 2019 monsoon would help conserve enough water for the city. By the beginning of June, the municipal corporation had to start dipping into the lakes’ reserve stocks to continue supplying water to Mumbai.

The start of this year’s monsoon has not proved promising enough. Even though three days of intense rainfall at the start of July led to civic chaos and several deaths in the city, the catchment areas of Mumbai’s reservoirs did not receive enough rain to help significantly increase their water levels.

On July 4, the seven lakes – Vihar, Tulsi, Bhatsa, Tansa, Upper Vaitarna, Middle Vaitarna and Modak Sagar – had a stock of 1.7 lakh million litres of water, which is only 12.02% of their total holding capacity. This is much less than the 22.4% of stock that the lakes held on the same date in 2018. In a bid to keep conserving water, Mumbai’s municipal corporation has not yet rolled back the water cuts to the city’s residents.

At a time when erratic rainfall is the new normal and reservoirs supplying water to major Indian cities are drying up, saving water through on-site methods like rainwater harvesting becomes increasingly crucial.

But in Mumbai, even though the rule for rainwater harvesting exists on paper, civic authorities have shown little inclination to take it seriously and ensure its implementation.

Where is the data?

Rainwater harvesting in buildings involves collecting rainwater on roofs and other open surfaces and directing it to large underground tanks or aquifers for storage and reuse. Collected rainwater can also be used for groundwater recharging.

Up till two decades ago, Mumbai had several wells scattered across the city and suburbs that residents used to draw groundwater. However, with rapid concretisation of the city, most of these wells are now out of use and the city’s groundwater has depleted significantly over the years.

“Groundwater recharge is very important, but has become difficult because concretisation prevents rainwater from percolating into the ground,” said Indrani Malkani, a trustee of V Citizens’ Action Network, a non-profit organisation working for civic rights in Mumbai.

Storing rainwater in tanks is a more viable form of rainwater harvesting in Mumbai, but there is little information about the success of its implementation in the city’s new buildings.

In April 2016, when Mumbai was facing 20% water cuts before the monsoon, theHindustan Times reported that between 2007 and 2015, only 1,848 buildings out of an estimated 5,000 new constructions in the city had rainwater harvesting systems in place. This meant that only 36% of new buildings in the city had, at the time, followed the municipal corporation’s rule.

Scroll.in attempted to obtain the latest figures on rainwater harvesting systems in new constructions, but officials in the municipal corporation’s water supply department and rainwater harvesting cell were not available for comment. Several environment and civic experts confirmed that Mumbai’s municipal corporation does not maintain records on rainwater harvesting implementation in the city.

“The corporation’s rainwater harvesting cell should have been a part of its water supply department, but it has always been independent,” said TV Shah, a former hydraulics engineer with the Municipal Corporation of Greater Mumbai, who retired in 2005. “Since 2002, when the rule [about rainwater harvesting in new buildings] was first enforced, the corporation has not conducted any study on how efficiently it has been implemented or how much water has been saved.”

‘People are willing to pay for tankers’

Having rainwater harvesting systems in place in a building does not automatically mean that residents of the building or housing society are actually using the stored water. Like Sumesh Lekhi’s housing society in Versova, many buildings with rainwater harvesting facilities find that the water they store gets contaminated over time.

While these problems could be addressed through regular cleaning and maintenance of rainwater storage tanks, experts claim that the municipal corporation does not strictly monitor or enforce this, and few citizens have the will or interest to implement rainwater harvesting proactively. When water supply is low, most citizens find it more convenient to call for water tankers, even though the tanker industry plays a huge role in depleting groundwater resources.

“At the end of the day, people are willing to pay for tankers instead of looking at long-term solutions like maintaining rainwater harvesting systems,” said Debi Goenka, an executive trustee of Conservation Action Trust, an environmental rights group.