In the solid breeder blanket of fusion reactor, bred tritium is planned to be extracted from the blanket as HT by passing of H2-added sweep gas in general. In that case, tritium leakage by permeation to coolant can not be ignored. So, the application of H2O-added sweep gas is discussed, with which tritium leakage to coolant can be much reduced. As the result of discussion, H2O-added sweep gas is probable method of tritium recovery. For the further detailed discussion, it is important to enrich the data correlated to the interaction of H2, H2O, breeder, multiplier and structures.