TiO2 photocatalytic oxidation of a mixture of four pharmaceutical emerging contaminants (ECs): caffeine, flumequine, ibuprofen and carbamazepine, has been studied both in ultrapure and municipal wastewater with the main aim of checking the direct and indirect transfer mechanism of this process. Also, given the high importance of knowing the volumetric rate of photon absorption (VRPA) for the kinetics of the process, actinometrical results have been compared to those from the six flux model (SFM) application. Finally, kinetic equations derived from the direct and indirect transfer mechanism of photocatalytic oxidation have been deduced to fit experimental results and conclude about the possible removal way of ECs in water when this advanced oxidation process is applied.