A water-heating solar parabolic collecting and concentrating apparatus comprises a pair of inclined parabolic reflectors positioned side by side on a rotary framework with upwardly extending water-heating tubes positioned along the focal lines of the respective reflectors. The tubes are split longitudinally into forward and reverse flow water passages by vanes which also provide heat transfer enhancing fins projecting diametrically from the tubes. Inlet and outlet hoses from the respective tubes extend through a turntable base forming part of the framework on which the collectors are mounted, for rotational sun-tracking under the power of a timer-controlled electric motor.