A theoretical study of applicability of double-membrane reactor for direct thermal decomposition of water is presented. The analysis is based on an isothermal, steady state, plug flow reactor model. One of the two membranes was supposed to be hydrogen permeable, and the other one, oxygen permeable. The simulations were performed for T=2000 K, it being the upper limit of temperatures of practical interest. With a high vacuum in separation zones, the double-membrane configuration theoretically enables complete conversion providing high values of Damkohler number and total rate ratio. When a sweep gas is introduced into separation zones, significant water conversions can also be provided by a countercurrent single membrane reactor, but considerably lower than those obtained in a double-membrane reactor. The double-membrane reactor seems to be a promising solution for the water splitting reaction, deserving experimental investigations.