The Star Trek Project : Technology : Sonic Shower
The sonic shower is a very important device, used by billions of Federation citizens every single day. It provides a faster, cleaner, and more efficient way to cleanse oneself every morning.
It works on simple principles. Very low frequency vibrations are generated, and projected at the subject. These vibrations pass through an acoustic inverter, to ensure that they are not harmful to the humanoid in the shower, then they shake any foreign particles off of the skin and hair of the showeree, and are then sucked away through a few small vacuums.
The most prominent problem with sonic showers is that the acoustic inverters have been known to short out, which can cause an uncomfortable experience for whoever is cleaning at the time. The effects can range from a tingling sensation on the skin to actual physical bruises appearing.