Fumonisins are known as secondary metabolites of the mold Fusarium verticillioides that most often contaminate cereals and animal feed. According to recent research, these mycotoxins have also been detected in the aquatic environment, which may be the result of washing off the crops during rainy periods, or because of their possible production in the water. Since fumonisin B₁ (FB₁) is highly toxic and has dangerous effects on the health of living organisms, in this research the influence of different water matrix on the effectiveness of UV and UV/H₂O₂ treatments was investigated. Namely, different water types (water from Danube River, tap, and underground) were simulated with the addition of humic acid and major ions for each type of water into ultrapure water (UPW). Results showed a lower removal efficiency of FB₁ by direct UV photolysis in the simulated water samples in comparison to the UPW. In the case of UV/H₂O₂ treatment, the efficiency of FB₁ removal in simulated waters was also lower compared to UPW. However, this treatment was more effective than direct photolysis. Namely, in UPW 100% of FB₁ removal was achieved after 90 min of irradiation, while among the investigated simulated water samples the highest removal efficiency was reached in tap water, when 50% of FB₁ was degraded after the same time of irradiation. These results provide insight into the influence of the matrix of different water types on the efficiency of FB₁ removal and contribute to the development of adequate water purification methods for potentially carcinogenic fumonisins.