The sonic shower introduced in ST:TMP
was conceptually based on a real-world "hydrosonic shower" prototype unit developed at - IIRC - McDonnell Douglas Astronautics' Huntington Beach, California facility circa 1976 under a study contract to Jesco von Puttkamer's office at NASA-OSF in order to minimize the amount of liquid water storage required for long-duration manned space missions. A description of the system was also published by its designers in one of the early AIAA Space Manufacturing
volumes edited by Jerry Grey. I don't have my copy handy, but the mechanism employed steam jets and high-frequency (ultrasonic), low-amplitude acoustic generators to bathe the user in a thin film of water condensate which would then be vibrated, thus initiating the cleansing function. A few drops of liquid soap was all that was required to dissolve whatever sweat and dirt had accumulated since the last "shower", but further development of the hardware was apparently never pursued due to the excessive mass, complexity and cost of the original, to say nothing of the catastrophic budget cuts during the 1970s that destroyed NASA's plans for manned spaceflight beyond STS. The idea itself is absolutely sound (heh) though, as none of the MDA engineers who subjected themselves to the prototype reported any discomfort or injury during testing.