Water breeder reactors based on thermal water reactors have the advantages of a well-proven technology, a wide operational experience, and an acceptable safety status, the latter from using water as a coolant and having a negative void coefficient. Water breeder reactors are now in operation for the 232Th-233U cycle and are being designed for the 238U-Pu cycle. This paper proposes a water breeder system in which two reactors operate in symbiosis, one using 238U-233U as fuel and producing plutonium, and the other using 232Th-Pu as fuel and producing 233U. Thus, each reactor feeds the other. From the breeding point of view, the combined system has an advantage over the separate 238U-Pu and 233Th-233U cycles.