This doesn't help you see how it works with electricity, because it's not really how it's done with electricity. Put two valves after each other on a pipe. The

This doesn't help you see how it works with electricity, because it's not really how it's done with electricity. Put two valves after each other on a pipe. The water can only flow if the first valve AND the second valve are open. Fork off a pipe into two pipes with a tee, put a valve on each side, and connect the other ends of the valves together with another tee. Water flows through the whole thing if the first valve OR the second valve is open (or both). That's how it works with electricity too. The valves are themselves controlled with water/electricity too.