A dimensionless mathematical model for a novel, thin film, slurry fountain photocatalytic reactor for water or wastewater treatment is presented. The model extends the applicability of the horizontal water fountain model previously presented to include water fountains with a parabolic profile. The model was developed using parameters that can be easily estimated for real systems. The model was successfully validated with experimental results from the photocatalytic oxidation of indigo carmine dye in a pilot-scale reactor using titanium dioxide (TiO2) as the photocatalyst.