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 (61 m) beneath the lake, varying in shape from circular to oval, and ranging in diameter from 10 to 20 feet (3.0 to 6.1 m). The tunnels lead from the water cribs to Pumping Stations located onshore, then to water purification plants Jardine Water Purification Plant (the world's largest) and the Sawyer Water Purification Plant (operating since 1947), where the water is then treated before being pumped to all parts of the city as well as 118 suburbs.
The city has had nine permanent cribs of which six are still standing and two are in active use.