The aim of this paper was to determine the efficiency of a rainwater treatment installation located near the farm buildings of Roztocze National Park (RNP), Poland. The rainwater treatment system, consisting of two polypropylene filters, one activated carbon filter and a UV lamp, was examined. Samples of raw and treated rainwater were collected once a month from June to December 2023. The study shows that average efficiency of pollutant removal in the analysed rainwater treatment system was not very high and amounted to 38.8% for ammonia, 29.6% for turbidity, 27.9% for NO2, 19.8% for NO3, and 6.9% for copper. The low efficiency values can be explained by the low concentration of these parameters in rainwater from the tanks. The efficiency of removing microbiological contaminants was very high and ranged from approximately 98% to 100%. It was shown that the UV lamp ensures very good disinfection of rainwater. The study shows that rainwater treated using filtration and disinfection (UV lamp) can be used for watering the Polish Konik horses living in the park, as well as for washing vehicles, watering green areas, or flushing toilets. The present findings can be used in the design of a new system for managing rainwater that is planned to be built in the RNP’s Animal Breeding Centre, as well as to prepare other rainwater systems, especially in protected areas.