 Using the purification capacity of wetlands, the Indian city of Kolkata has pioneered a system of sewage disposal.Originally built to house one million (10 lakh) people, Kolkata is now home to over 10 million (over 1 crore) people, with nearly one-third of them living in slums.But the 8,000-hectare East Kolkata Wetlands Ramsar Site, a patchwork of tree-fringed canals, vegetable plots, rice paddies and fish ponds – and the 20,000 people that work in them – daily transform one-third of the city's sewage and most of its domestic refuse into a rich harvest of fish and fresh vegetables.