This study aimed to determine the relationship between the concentration of heavy metals in drinking water and the number of type 1 diabetes mellitus (T1DM) cases in two regions of Poland. The number of births in 2015-16 in Pomeranian Voivodeship was 50,461, while the number of new T1DM cases was 219. In Lublin Voivodeship, the number of births in the same period reached 39,381, and the number of new T1DM cases was 221. The incidence of T1DM, calculated per 100 live births, amounted to 0.43 and 0.56 in Pomeranian and Lublin. The statistical analysis of collected data proved that the number of new T1DM cases in Pomeranian Voivodeship is correlated to the concentrations of selenium (Se; p < 0.0001), lead (Pb; p < 0.00001), cadmium (Cd; p < 0.00001), zinc (Zn; p < 0.00001) and arsenic (As; p = 0.00001). In the case of Lublin Voivodeship, the number of new T1DM cases was correlated to the concentrations of Se (p = 0.0000001), Pb (p < 0.000001), Cd (p = 0.0000001) and Zn (p < 0.00001) in drinking water. No correlation was found between the number of new T1DM cases and arsenic concentration in the drinking water samples from Lublin Voivodeship. The results indicated that environmental exposure to specific heavy metals may contribute to the risk of T1DM, underscoring the need for stringent environmental controls and public health policies to mitigate these risks. Keywords: drinking water; arsenic; zinc; cadmium; lead; selenium; pH; children; type 1 diabetes mellitus