a water - powered sump pump that utilizes a relatively higher pressure water ported through a self - reversing valve to a reversible stroke power cylinder having a movable member mechanically coupled to a pumping chamber for movement of a movable pumping member in the pumping chamber , movement of the movable pumping member forcing sump water to a discharge . the volumes of the power cylinder and pumping chamber are different such that relatively high pressure , low volume flow to the power cylinder results in relatively high volume , low pressure flow from the sump pumping chamber . the discharge from the power cylinder is backflow prevented with respect to the discharge from the sump pumping chamber .