In this work, we studied the effect of inorganic ions occurring in natural waters on E. coli inactivation by solar and photo-Fenton processes, two crucial methods for drinking water treatment in sunny or developing countries. HCO3-, Cl-, SO42-, NO3-, NO2- and NH4+ were assessed at relevant concentrations for their inhibiting or facilitating role. The inactivation enhancement during solar disinfection (SODIS) was mainly attributed to the generation of HO center dot radicals produced during by excitation of NO3-, NO2-, while the HO center dot of photo-Fenton may be transformed into other radical species in presence of ions. Natural organic matter (NOM) was found to enhance both processes but also to hinder most of the enhancing ions, except for NO2-; modeling with the APEX software unveiled the inter-relations in the presence of NOM, and the possible inactivation activity by NO2 center dot. The photo-Fenton inactivation was more significantly enhanced by ions than SODIS (besides the case of NO3-, NO2-), but both processes were found robust enough.