Our study addresses three of the four factors noted in the Introduction that lead to the inefficient utilization of photogenerated holes. (1) Although it has been proposed that high recombination rates between holes and electrons can remove a considerable fraction of photogenerated holes before they can participate in oxidation reactions, this is not found in the simulations. Using the experimentally reported recombination rate coefficients, we find the losses of holes are very low with at most 8% recombined in the crystal bulk and even lower at the surface. This indicates that the losses do not significantly compete with the surface chemistry. (2) Surface defects and impurities have been proposed to trap photogenerated holes and prevent them from reaching the reaction sites. We have found that the introduction of bulk defects into the model has little or no effect on the hole concentration and surface hole photocurrent. There are many hole traps (Ti sites and bridge oxygen sites) all over the surface; it is unclear what other types of defects would be important and further information on their kinetic properties would be valuable. work may also apply to them. By careful management of the interplay between charge carrier dynamics in the semiconductor and thermal processes, it may be possible to improve their photocatalytic water splitting performance.