Having known the fact that on the territory of West-Backa region the only water used for water supply system is subterranean water, from different water layers, an assumption can be made that the waters also differ in their physical and chemical content. It is also assumed that these waters differ in their total iron content. The aim of this work is to test the significance of the difference between central water supply systems of West-Backa region (Sombor, Apatin, Kula and Odzaci) for the value of iron in drinking water, using the adequate statistics methods. The central water supply systems in Sombor, Apatin, and Kula are using water from the second water layer (60-75 m), while the water supply system in Odzaci is using deep artesian and subartesian waters (146-220 m). Sombor and Apatin have the raw water purification system and one of the goals is to decrease the concentration of total amount of iron in drinking water.