The possibility of the use of the laminar falling film slurry type photoreactor was examined in conjunction with ZnO as a photocatalyst for the removal of thiacloprid (TCL) from Calypso 480-SC commercial formulation by UV radiation. The degradation kinetics were monitored by HPLC DAD, while the disappearance of the nitrile group, i.e. TCL and intermediates containing this group, was followed by FTIR The study of TCL removal under different operating conditions indicated that 2 g/L of ZnO was an optimal catalyst loading, and the optimal pH was 6.8. In the investigated range of initial concentrations of TCL (0.05-0.38 mM), the photocatalytic degradation in the first stage of the reaction followed approximately a pseudo-first-order kinetics. The increase of LTV-light intensity resulted in a linear increase in the rate of TCL degradation. The figure-of-merit electrical energy per order was employed to estimate the electrical energy consumption. Because the efficiency of TCL photodegradation in the natural thermal water was about two times lower than in distilled water, the investigation encompassed the influence of the thermal water components, i.e. different inorganic ions and humic acid, on the rate of TCL degradation.