The application of a photocatalytic water treatment reactor to initiate the desired reaction is a relatively new area of research, but the growing number of recent publications shows an increasing interest. In order to utilize solar UV and visible light, flat-plate photocatalytic reactors are generally regarded as efficient as they provide high surface area to volume ratio for water treatment. However, the operating of a photocatalytic reactor in a non-uniform flow field results in a highly non-uniform local rate of reaction. This emphasizes the need for flow field investigation in the design and optimization of photocatalytic reactor for water treatment. Reliable modelling of the reactors flow structure is therefore crucial for the efficient design of the device. This paper aims to investigate a detailed computational fluid dynamics (CFD) analysis of a novel flat-plate photoreactor. Simulation results obtained using various turbulence models and reactor inlet configurations for various flow rates are presented. The influence of inlet positions and three different turbulence models: Standard k-, Realizable k- and Reynolds stress model (RSM) on the simulation results are also evaluated.