Cd, Cr, Cu, Hg, Ni, Pb and Zn, and metalloids as As and Se, have long been contaminants of residues originated from water and wastewater treatment processes. They are concentrated to residual sludges from potabel waters, effluents or sewages and the treatment chemicals. Most of the elements referred here are classified as priority pollutants. Though the main objective is achieving compliance with the legislations in water and effluent quality - drinking and surface waters - more and more attention is paid to residual disposal and also to sludge quality. To avoid contamination by chemicals used in such treatments their quality has also been regulated in drinking water treatment but it is not strictly controlled in the treatment of industrial effluents. Heavy metal contamination of the residual sludge is supposed to be mainly resulted from the high contamination of sewages in case of municipal sewage treatment.