India, April 20 -- Perched atop a truck under the bright afternoon sun, 50-year-old Pramod Mandal moves swiftly, stacking freshly harvested cauliflowers one over the other as workers below pass up basket after basket. The 20-acre field in southwest Delhi's Dichaon Kalan operates with a quiet efficiency - a ladder propped against the truck, men climbing up and down in rapid succession, the vehicle gradually filling up with what will soon be nearly 30 quintals of produce bound for mandis in Keshopur or Azadpur.

Just beyond the field, the Mungeshpur drain - a supplementary channel of the Najafgarh drain snakes past in a near-pitch-black stream, its surface heavy with industrial effluents. While Mandal is reliant on groundwater, there are pl...