that is typically less water is collected for use it is thus envisioned by the invention to fully utilize rain falling on the sea or the like rain is collected and stored by a novel floating reservoir on the water water stored in the reservoir on the water can be utilized to generate electricity if its quantity is sufficient also water can be further utilized to bring a water supply to a city factories or farmland referring to fig1 again a system of collecting water and generating electricity by a reservoir on the water in accordance with another preferred embodiment of the invention is shown the system is built on the sea in this embodiment however the system can be also built on a lake or a conventional reservoir in other embodiments the system comprises a reservoir 82 on the water formed of frp having properties of low density high strength and being corrosion resistant one or more of hollow buoyant members 81 filled with materials having a density less than water e g cork and formed under the reservoir 82 as means for supporting the reservoir 82 on the water a plurality of steel ropes 83 each having one end fastened at bottom of the reservoir 82 the reservoir 82 and buoyant members 81 are secured.