From the almighty Wikipedia :
"A navy shower (or "sea shower") is a method of showering that allows for significant conservation of water and energy by turning off water during the "middle" portion. An initial thirty seconds or so are used to get wet, followed by soap and lather, which is then rinsed off in a minute or less. The total time for the water being on is typically under two minutes.
Navy showers originated on naval ships, where supplies of fresh water were often scarce. Using this method, crew members were able to stay clean, while conserving their limited water supply. The idea has been adopted by many people who wish to conserve water and the energy needed to heat the water, for both environmental and economic reasons. Maritime cruisers often take navy showers when they are not in a port with easy access to fresh water. A ten-minute shower takes as much as 230 L (60 U.S. gallons) of water, while a navy shower usually takes as little as 11 L (3 U.S. gallons); one person can save 56,000 L (15,000 U.S. gallons) per year."