Water tower

BB came into our bed this morning, as we tried to sleep-in a bit. He had water towers on the mind and the amount of pressure they exert on the water. What happens, he wondered, if one doesn't open a faucet for a long time? Does the pressure build up and finally break the faucet's valve? I talked about the steady state of the water and its pressure. He still wasn't satisfied. Doesn't it go boom? (He's fascinated with explosions, which the show Mythbusters only stokes.) His mom brought up water balloons and how they will burst if you fill them too much. I then tried to talk about the relative strength of the materials used to hold water. But BB was running with his mom's thought experiment. Can we make them go boom?