NOVELTY - The water tower includes a reservoir (20) which has a bottom surface (21). A recirculating passageway (60) is fluidly connected to reservoir. The recirculating passageway includes a first end (61) connected to and located near or below the bottom surface of reservoir, and a second end (62) connected to the reservoir above bottom surface. A pump (63) is located in the recirculating passageway, and pumps fluid through recirculating passageway. A fluid-driven energy generating device (40a,40b) is fluidly connected to at least one of recirculating passageway or fluid discharge passageway (30).    USE - Water tower for supplying water and used in power generation system (claimed).    ADVANTAGE - Encourages the community for more efficient use of power, and helps reduce pollutants since a real-time display is provided on the water tower to continuously show power information, e.g. power saved and power cost savings from the operation of power generation system, reductions in carbon dioxide and other pollutants and contributors to global warming from the system. Reduces pumping cost since renewable energy is generated in the day or night using solar arrays and wind turbines, and other energy is generated from the flow of fluid into and from the reservoir. Improves the efficiency of the electric grid since providing higher prices during peak periods sends more transparent market signals. Avoids requiring more expensive power storage systems since excess power generated by the power generation system is captured and sold to the electric grid.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) an operating method of power generation system; and    (2) a power generation system    DESCRIPTION OF DRAWING(S) - The drawing shows a perspective view of the water tower used in the power storage and generation system.    Reservoir (20)    Bottom surface (21)    Fluid discharge passageway (30)    Energy generating device (40a,40b)    Recirculating passageway (60)    First end (61)    Second end (62)    Pump (63)