According to the Wikipedia article, a navy shower (aka "sea shower") is a method that saves alot of water and energy. It involves turning on the water just long enough to wet the body, turning off the water. soaping up [or shampooing, whatever] and then turning the water on to immediately rinse off the soap/shampoo, then turning the water off. The total time for navy showers is typically 2 mins, almost always under 5.
As the site greenasathistle.com states, this concept means that: "while you’re standing there fussing with shampoo bottles and getting all sudsy, there isn’t any excess water going down the drain. By the time you’ve finished, the H2O should’ve only been running for about two minutes.
This idea originated on naval ships, where, ironically, supplies of fresh water were often scarce — now, many modern hippies have taken it up for both environmental and economic reasons. Whereas a 10-minute shower uses as much as 230 litres of water, a properly done navy shower usually only requires just over 10 litres, which means that over the course of a year, a single person can save up to 56,000 litres of this precious resource."
Beginning with my shower tomorrow morning I am implementing this change.