India, Oct. 27 -- Once celebrated as the Garden City, Bengaluru has watched its lakes shrink and its canopy thin under the weight of relentless urban growth. But one man's determination is helping the city reclaim its green soul.

On Sunday, Prime Minister Narendra Modi, in his Mann Ki Baat address, applauded Kapil Sharma, a Bengaluru-based engineer, for leading a quiet but powerful environmental movement. Sharma's work, reviving neglected wells and lakes and rallying citizens and companies to join hands, has become a model for sustainable urban action.

Originally from Raipur, Sharma moved to Bengaluru in 2001 for his engineering studies and was instantly enchanted by its tree-lined avenues. But by 2005, he noticed an unsettling pattern,...