The trouble with camping, boating, fishing and being outdoors and away from home is that if you get dirty, or hot, or uncomfortable, which you know you will, about the best you can do is dream longingly of a refreshing shower, or jump into a cold stream or lake--if one is nearby. Now welcome Sun Shower, a heavy-duty black plastic bag that generates sun- warmed hot water, and is equipped with an efficient nozzle for showering. Fill it with 21/2 gallons of water, leave it face up in the sun, then hang it up and enjoy enough warm water for two adults to shower. The manufacturer claims 60-degree water will reach more than 100 degrees in three hours, but sailors on the Chesapeake Bay found that 70-degree water will heat to about 100 degrees in three hours on a typical June or September day. The heating process depends on exposure to direct sunlight. Water won't heat as fast on partly cloudy days and hardly at all on overcast days. A sensor dot on the bag indicates when the water temperature hits 90 degrees. The device can heat water well into the 120-degree range-- so be careful on very hot, sunny days. Once the water has reached about 100 degrees, the bag can be turned over and it will usually maintain the water temperature. After sundown the water will stay hot for hours if the Sun Shower is wrapped in a sleeping bag. The shower rolls up easily and weighs less than a pound when empty, for easy carrying.

Sun Shower. $13.95. At many marine supply stores, camping stores and from Basic Designs Inc., Box 479, Muir Beach, Sausalito, Calif. 94965.