The photodissociation of H2O in its B band is a prototype for nonadiabatic reaction dynamics. In addition to dissociation via the adiabatic pathway to the OH(Ã(2)Σ(+)) + H fragments, it also produces the OH(X̃(2)Π) + H fragments through two nonadiabatic pathways: the B̃ → X̃ transition via two conical intersections and the B̃ → Ã transition via a Renner-Teller pair. In this work, the state-to-state dissociation dynamics in all three channels are investigated with a full-dimensional quantum mechanical model using a set of coupled diabatic potential energy surfaces determined at the internally contracted multireference configuration interaction level with the aug-cc-pVQZ basis set. The inclusion of all relevant electronic states not only results in an improved agreement with the latest experimental data but also sheds valuable insights into the competition between the two coexisting nonadiabatic pathways.