Knowledge of the frontier levels' alignment prior to photoirradiation is necessary to achieve a complete quantitative description of HO photocatalysis on TiO(110). Although HO on rutile TiO(110) has been thoroughly studied both experimentally and theoretically, a quantitative value for the energy of the highest HO occupied levels is still lacking. For experiment, this is due to the HO levels being obscured by hybridization with TiO(110) levels in the difference spectra obtained via ultraviolet photoemission spectroscopy (UPS). For theory, this is due to inherent difficulties in properly describing many-body effects at the HO-TiO(110) interface. Using the projected density of states (DOS) from state-of-the-art quasiparticle (QP) GW, we disentangle the adsorbate and surface contributions to the complex UPS spectra of HO on TiO(110). We perform this separation as a function of HO coverage and dissociation on stoichiometric and reduced surfaces. Due to hybridization with the TiO(110) surface, the HO 3a and 1b levels are broadened into several peaks between 5 and 1 eV below the TiO(110) valence band maximum (VBM). These peaks have both intermolecular and interfacial bonding and antibonding character. We find the highest occupied levels of HO adsorbed intact and dissociated on stoichiometric TiO(110) are 1.1 and 0.9 eV below the VBM. We also find a similar energy of 1.1 eV for the highest occupied levels of HO when adsorbed dissociatively on a bridging O vacancy of the reduced surface. In both cases, these energies are significantly higher (by 0.6 to 2.6 eV) than those estimated from UPS difference spectra, which are inconclusive in this energy region. Finally, we apply self-consistent QPGW (scQPGW1) to obtain the ionization potential of the HO-TiO(110) interface.