Electrical power is generated from falling liquids such as captured rain water, gray water and black water in tall buildings using two or more reservoirs. Fill valves for each of the reservoirs are controlled to fill the first reservoir in a raised position while emptying the second reservoir in a lowered position. When full, the first reservoir is dropped to the lowered position while imparting mechanical energy to an electrical generator and while raising the second reservoir. Next, the second reservoir is filled until full while the first reservoir is emptied, followed by dropping the second reservoir to the lowered position while imparting mechanical energy to the electrical generator and while raising the first reservoir. The cycle is repeated so that electrical generation from the falling of the liquid avoids the liquid contacting or passing through a turbine or impeller.