A water pump includes a base, a cam, a joint, and a piston. The base includes a PTO-attachment portion, a cam-attachment portion, a first contact surface, and a second contact surface. The cam includes a central opening, a first cam contact surface, and a second cam contact surface, wherein the cam-attachment portion of the base extends into the central opening. The joint pivotally couples the cam to the cam-attachment portion of the base. In a first operating position of the cam, the first contact surface engages the first cam contact surface so that the cam is positioned at a first angle relative to the axis of PTO rotation. In a second operating position of the cam, the second contact surface engages the second cam contact surface so that the cam is positioned at a second angle, greater than the first angle, relative to the axis of PTO rotation.