If water costs more, that's a signal to entrepreneurs to invest money into methods of providing water, and also a signal to everyone to conserve water, both of

If water costs more, that's a signal to entrepreneurs to invest money into methods of providing water, and also a signal to everyone to conserve water, both of which are exactly what you should want if you're worried about the supply of water. The issue of very poor people being unable to afford water is obviously important, but completely separate.