India, Sept. 18 -- For Ajay Singh, conversations about pollution and mounting waste were not just talk.

An information technology professional who runs a cybersecurity firm, the 51-year-old resident was troubled by the amount of untreated water, food waste and plastic routinely ending up in landfills. When he became the resident welfare association (RWA) president of Tulip Ivory in Gurugram, he saw an opportunity to test a simple idea: could a housing society treat its waste?

His first intervention was wastewater. Singh focused on upgrading the society's sewage treatment plant (STP), ensuring that not a single drop of untreated wastewater flowed out of the premises. The society began reusing treated water, reducing dependence on fresh w...