This paper presents the variability of the quantity and specific composition of the sludge produced at two different surface water treatment plants ‒ the Raba water treatment plant (WTP), collecting water from an artificial reservoir; and the Rudawa WTP, collecting running surface water. The authors analyzed the differences in the amount and characteristics of sludge and tried to relate them to specific technological systems in use at the treatment plants. The paper mainly focuses on heavy metals removed from the water and then trapped in the sludge. The aim of the work was to describe changes that involved both the quantity of sludge and its characteristics, especially with respect to its further disposal (e.g. heavy metals, etc.). Additionally, some aspects of an activated carbon dosing regime and its impact on a heavy metal content in sludge were discussed.