The photo(electro)chemical production of hydrogen by water splitting is an efficient and sustainable method for the utilization of solar energy. To improve photo(electro)catalytic activity, a Schottky-type barrier is typically useful to separate excited charge carriers in semiconductor electrodes. Here, we focused on studying the band: diagrams and the Schottky-type barrier heights of Ta3N5, which is one of the most promising materials as a photoanode for water splitting. The band alignments of the undoped and n-type Ta3N5 with adsorbents in a vacuum were examined to determine how impurities and adsorbents affect the band positions and Fermi energies. The band edge positions as well as the density of surface states clearly depended on the density of ON impurities in the bulk and surface regions. Finally, the band diagrams of the n-type Ta3N5/water interfaces were calculated with an improved interfacial model to include the effect of electrode potential with explicit water molecules. We observed partial Fermi level pinning in our calculations at the Ta3N5/water interface, which affects the driVing force for charge separation.