The New York City water supply system leaks at a rate of up to 36 million US gallons (140,000 m3) per day. A complex five-year project with an estimated $240 million construction cost was initiated in November 2008 to correct some of this leakage in the Delaware Aqueduct. The work includes underwater diving teams of six divers who live in a 24-foot (7.3 m) pressurized tube that includes "showers, a television and a Nerf basketball hoop" in conditions designed to replicate those of their underwater work site. The divers breathe air that is 97.5% helium and 2.5% oxygen. The six divers descend 700 feet (210 m) to the work site where they work 12-hour shifts at a time.
http://www.nytimes.com/2008/11/23/nyregion/23tunnel.html