The removal of arsenate [As(V)] and arsenite [As(III)] from water was investigated by using reverse osmosis (RO) technique with SWHR and BW-30 (FILMTEC) membranes. The effect of pH and concentration of the feed water and operating pressure on the rejection of both arsenic species was examined. The experimental results indicated that rejection for both As(V) and As(III) mostly depended on the membrane type, pH of the feed water and operating pressure. For both membranes. As(V) rejection was maximum at pH above 4.0, while As(III) could be effectively removed from water at pH above 9.1. The rejection for both arsenic species increased with increasing operating pressure. The lowest permeate concentration of As(III) and As(V) was obtained when SWHR membrane was used. Finally, a natural (ground) water sample containing 50 mu g/L of As(V) and 12 mu g/L of As(III), respectively was treated by using RO with SWHR membrane. The obtained permeate concentration of total arsenic was compared with WHO and EU standards and permeate fluxes were evaluated by considering the chemical composition of the groundwater sample. (C) 2011 Elsevier B.V. All rights reserved.