Abstract Alumina-containing water potabilization sludge (WPS) is one of the main wastes produced by reservoir management activities. This kind of residues, deriving from treatment processes for water potabilization, recently attracted great attention as starting raw material in the production of innovative building materials. In this study, the use of WPS as aluminosilicate source for the synthesis of geopolymers has been investigated. In particular, two different potabilization sludge deriving from the water treatment plants of two artificial water reservoirs have been selected. For both of the WPS, mineralogical (XRD analysis), physical-chemical (FTIR analysis), thermal (TGA-DSC analysis), porosimetric (BET analysis) and morphological (SEM analysis) properties have been evaluated. A thermal treatment at 650 °C has been performed on the two raw sludge in order to increase their reactivity. Geopolymeric samples have been produced by the hardening of the calcined WPS in two sodium silicate solutions, differing only by concentration, and using two curing temperatures. Obtained specimens have been widely characterized from chemical, mechanical and microstructural points of view. SEM, FTIR and XRD analyses confirmed that the geopolymeric reaction effectively took place for the samples produced by using the more concentrated solution and the higher curing temperature. In general, the mechanical performances reached by the specimens, suggest the possibility of a promising reuse of WPS as raw materials for the synthesis of geopolymer based building precast components.