But a water tower only has one terminal. A better "capacitor" would be a pair of water towers side by side. To "charge" this double-water-tower capacitor, pum

But a water tower only has one terminal. A better "capacitor" would be a pair of water towers side by side. To "charge" this double-water-tower capacitor, pump some water from one to the other. And, when the water-tower capacitor is entirely "discharged," the towers both have the same water level inside. (As with a real capacitor, the total amount of water never changes.)