Hows about this idea? Use a garden sprinkler timer. They're already setup to attach with garden hose type fittings and already contain the right kind of valve. Time for a shower or washing dishes or laundry set the timer for a few hours and done. No need to remember to turn it off, or work with any wiring.
Other than that, lawn sprinkler diaphragm valves are rated for 24 volts AC but work just fine with 12 volts DC. Get a 3/4" valve and some NPT to garden hose fittings and then wire the switch up wherever. Although not specifically advertised as drinking water safe, I don't see anything inside a sprinkler valve that would be toxic. The body is PVC and the diaphragm is neoprene.
