An underground porosity water storage reservoir minimizes the impacts on surface uses of the reservoir site. Furthermore, a method of operating an underground porosity storage reservoir minimizes damage to the reservoir due to injecting sediment-laden water or water that is chemically incompatible with the porous material in the underground reservoir. The underground porosity water storage reservoir reduces temperature impacts on surface waters due to the discharge of stored water. A method of using the porosity storage reservoir to minimize adverse temperature impacts when discharging water to a surface body is disclosed.