In total, 36 environmental water samples were collected in 2012‒2014 from the area of two neighbouring provinces in Poland, Pomerania (in the north) (n = 16) and Warmia-Masuria (north-eastern part of the country) (n = 20). In total, 26 water samples were taken from 13 surface water reservoirs and ten water samples from five surface wells 5–7 m in depth (Table 1, Figure 1). Surface water samples originated from 11 lakes, including Choczewskie, Żarnowieckie, Wysockie, Sitno, Dłużecko, Osowskie, Dobre, Rydzówka, Mamry, Jeziorak, and Pozorty, a pond, and the Vistula Lagoon (Figure 1). Most of the lakes selected for investigations are often used as recreational sites for tourists and local inhabitants, with watering places, guesthouses and campgrounds in the vicinity. The lakes differ in terms of surface area and water quality. The Vistula Lagoon, also used for water sports and recreation, is a brackish-water lagoon on the Baltic Sea roughly 90 km long and 10 to 19 km wide, separated from Gdańsk Bay by the Vistula Spit. The lagoon serves as the mouth of several branches of the Vistula River and is connected to Gdańsk Bay via the Strait of Baltiysk. All wells, as well as the pond, examined in this study are located in homesteads (gardens/yards) situated in small villages in Warmia-Masuria province. According to the owners, water from these wells is not used for drinking; however, it might be used to water plants in kitchen gardens.