I’ll tell you what would be the best invention...
A shower water valve with a pushbutton on/off switch. I have no problem with shutting the water off whilst soaping up and then turning it on again to rinse (this was required for showers when I was on a submarine)...except that it sucks having to readjust the cold and hot water to get the temp right when turning the water back on—to the point where I don’t turn the water off.
If there was a valve with an off switch, so that you didn’t have to readjust water temp when you turn the water back on, this would not be a problem. Maybe there already is such a device...don’t know, but it would save a heck of a lot of water.
“If there was a valve with an off switch”
A solenoid valve like in a dish washer or washing machine would work. For that matter, if you had two valves you could pulse width modulate them so you could adjust the temperature digitally. Set the temperature only once, and it would always be correct.
**”A shower water valve with a pushbutton on/off switch. I have no problem with shutting the water off whilst soaping up and then turning it on again to rinse (this was required for showers when I was on a submarine)...except that it sucks having to readjust the cold and hot water to get the temp right when turning the water back on—to the point where I don’t turn the water off.”**
That is a common $5.00 and $20.00 item, and is often free.
https://www.google.com/search?newwindow=1&es_sm=93&biw=1440&bih=813&tbm=isch&sa=1&q=shower+head+with+flow+button+button&oq=shower+head+with+flow+button+button&gs_l=img.3...31847.38541.0.38829.24.23.0.0.0.5.551.3402.2-3j3j1j2.9.0.msedr...0...1c.1.64.img..23.1.550.edfTO8AE-Qg