Global potential energy surfaces for the three lowest electronic triplet states of O(P-3) + H2O((1)A(1)) are used to explore two unusual reaction pathways, not previously identified. Both pathways go through a D-2h rhombus geometry, with zero potential gradient and two imaginary frequencies. Motion along one imaginary frequency leads to O + H2O, while motion along the other leads to OH + OH. In each case, an O-atom is exchanged. Classical trajectory methods are used to compute exchange cross sections up to 11 km s(-1). Transition state theory rate constants for O-atom exchange processes are also computed. (C) 2011 Elsevier B.V. All rights reserved.