The effect of aluminum polynuclear hydroxo complexes on the coagulation of turbid and colored waters has been determined. The theoretical backgrounds regarding the expediency of forming mono– and polynuclear aluminum hydroxo complexes in coagulating natural waters of various composition were formulated. The joint use of aluminum sulfate and sodium hydroaluminate for the treatment of turbid and colored waters was analyzed; their efficiency was estimated in comparison with the basic coagulant. In addition, a hypothesis of the interaction mechanism of organic acids with polynuclear hydroxo complexes in the process of coagulating the colored water from surface water sources has been proposed.