Geothermally influenced waters are frequently found to be contaminated with arsenic (as As(V)). This study investigated the effect of high-temperatures (50°C), as found in geothermal source waters, on the rejection of monovalent H 2 AsO 4 − https://s3-euw1-ap-pe-df-pch-content-public-u.s3.eu-west-1.amazonaws.com/9781351046633/8978195a-ffaa-498f-8e06-bee4769ddb72/content/eq186.tif"/> and divalent HAsO 4 2 − https://s3-euw1-ap-pe-df-pch-content-public-u.s3.eu-west-1.amazonaws.com/9781351046633/8978195a-ffaa-498f-8e06-bee4769ddb72/content/eq187.tif"/> species (at pH 6 and 8) during NF membrane filtration of a multi-component solution containing Cl and HCO 3 − https://s3-euw1-ap-pe-df-pch-content-public-u.s3.eu-west-1.amazonaws.com/9781351046633/8978195a-ffaa-498f-8e06-bee4769ddb72/content/eq188.tif"/> . In this multi-component solution As(V) rejection was found to be enhanced at higher temperatures, whereas so far it was assumed that temperature rise had a negative effect on As(V) rejection. Previous studies were conducted with ultrapure waters, where pore size expansion dominated As(V) rejection, however, in the presence of other anions – like in natural water – As(V) rejection is promoted at higher temperatures. The enhancement of As(V) rejection at high temperature was associated with the presence of HCO 3 − https://s3-euw1-ap-pe-df-pch-content-public-u.s3.eu-west-1.amazonaws.com/9781351046633/8978195a-ffaa-498f-8e06-bee4769ddb72/content/eq189.tif"/> and Cl, which are considerably more permeable than both As(V) species. Additional advantage of the higher temperature was the lower feed pressure (down to 3 bar) needed to operate these NF membranes, compared to colder waters. Temperatures shows the potential application of this technology for efficient treatment of As(V) contaminated, geothermally influenced waters.