The objective of this study was to remove halides from waters by silver nanoparticles (AgNPs) and hydrogen peroxide (H2O2). The experimental parameters were optimized and the mechanism involved was also determined. The AgNP/H2O2 process proved efficacious for bromide and chloride removal from water through the selective precipitation of AgCl and AgBr on the AgNP surface. The optimal AgNP and H2O2 concentrations to be added to the solution were determined for the halide concentrations under study. The removal of Cl- and Br- anions was more effective at basic pH, reaching values of up to 100% for both ions. The formation of OH center dot, O-2(center dot-), radicals was detected during the oxidation of Ag(0) into Ag(I), determining the reaction mechanism as a function of solution pH. Moreover, the results obtained showthat: i) the efficacy of the oxidation of Ag(0) into Ag(I) is higher at pH 11, ii) AgNPs can be generated by the O-2(center dot-) radical formation, and iii) the presence of NaCl and dissolved organic-matter (tannic acid [TAN]) on the solution matrix reduces the efficacy of bromide removal from the medium due to: i) precipitation of AgCl on the AgNP surface, and ii) the radical scavenger capacity of TAN. AgNPs exhausted can be regenerated by using UV or solar light, and toxicity test results show that AgNPs inhibit luminescence of Vibrio fischeri bacteria. (C) 2017 Published by Elsevier B.V.