The shower head generally appears as any other but each tiny jet is individually controllable (on/off). A small video camera in the shower head feeds visual data to the CPU also within shower head.
The CPU recognizes the human body though the steam clouds and optionally performs a predictive analysis
of human motions. The jets are turned on just before someones arm/leg/body part moves to that position. For the most part your central body trunk doesnt move that much (easier or no prediction needed) and that is whats most uncomfortable when not being sprayed. When you leave the shower the spray stops. When the shower is first activated it will sense water temperature and allow warm up (full on), or just a time delay. Couples or a dog in the shower will be more difficult to analyze.
Gesture signals could be use to force full on/off mode for soaping up or head only/body only for shampooing, etc. No fussing with a dial to select spray patterns, use a gesture to select: concentric circles, random pulse etc.
So how to individually activate the nozzles: Muscle wires (flexinol) are currently too slow to track fast motions but would generally work (hot water would slow contraction), polymer muscles still in lab, micro solenoids etc etc. Mineral build up at the valves will be reduced with the frequent cycling.
Power to the unit could be a battery (I dont think 120 AC is so good here) or small turbine extracting some energy from the water flow (like an oscillating lawn sprinkler).
The water pressure could function as the return spring for each valve (if default is closed with water running). Default is nozzles open with full water pressure almost enough to close any valve so little power is required to close, once closed the water holds it shut so a small reverse power is all thats needed to reopen. If default was closed nozzles then with turbine there is no power to start (and a rechargeable battery could lose power if shower not used frequently or just out of box).
Not much benefit (and adding much to the complexity) we could have each nozzle steer able to concentrate the water for massage/extra to remove shampoo from head etc.
In addition it would be possible for the valve to vary the opening instead of on/off for hard and soft spray or to increase water conservation further.
Options: Built in Radio/iPod with gesture control of selection and volume, water spray pulses to music beat.
Additional search terms: Environment, Ecology, AI, Intelligent, Bath