The water cribs in Chicago are structures built to house and protect offshore water intakes used to supply the City of Chicago with drinking water from Lake Michigan. Water is collected and transported through tunnels located close to 200 feet beneath the lake, varying in shape from circular to oval, and ranging in diameter from 10 to 20 feet. The tunnels lead from the cribs to one of two water purification plants located onshore, the Jardine Water Purification Plant (the world's largest) and the South Water Purification Plant, where the water is then treated before being pumped to all parts of the city as well as 118 suburbs.