For environmental reasons, it is necessary to reduce emissions of plant protection agents (PPA). Emissions must be virtually zero in 2027 at the latest (EU Directive 2000/60/EC). In some countries legislation forces horticulture to have emissions reduced considerably well before that date (example NL 2018). The first (and most effective) measure to reduce emission should be reuse of water which is now emitted in the environment. This also saves fertilizers and water. Any remaining waste water should be treated to remove plant protection agents. A known method for drink water purification is UV oxidation: the combination of UV-C light and hydrogen peroxide (H2O2). Both UV-C light and H2O2 are well known in horticulture for disinfection purposes. Depending on the equipment UV-C dose and H2O2 dose may differ for optimal removal of PPA. Also, a minimal transmittance (T10) of the water for UV-C light is required. So, a grower should check his waste water for T10 before selecting the appropriate equipment. The required UV-C dose is ensured by measuring continuously the UV-C intensity and adapting the residence time of the water. The UV-chamber is kept clean by acid dosing at the end of the run, and acid injections during the operation can optimize capacity.