> I was always wondering why there are no systems converting the unused electricity in potential energy by moving water to a higher ground. And more importantly

> I was always wondering why there are no systems converting the unused electricity in potential energy by moving water to a higher ground. And more importantly: Why there are no water storages on the roof. Gravity is an incredibly feeble force, compared to electromagnetism (i.e. chemical bonds). Storing a practical amount of energy require a large mass × height.