A method for making a composite polyamide membrane comprising a porous support and a thin film polyamide layer, wherein the method comprises: i) applying a polar solution comprising a polyfunctional amine monomer and a non-polar solution comprising a polyfunctional acyl halide monomer to a surface of a porous support and interfacially polymerizing the monomers to form a thin film polyamide layer; ii) treating the thin film polyamide layer with a polyfunctional arene compound comprising 1 or 2 benzene rings collectively substituted with the following four functional groups: (a) a first functional group (w) selected from: -NR 4 R 5 and -OH, (b) a second functional group (x) selected from: -NR 4 R 5, -OH, -COOH, and-SO 3 H, (c) a third functional group (y) selected from: -H, - NR 4 R 5, -OH, -COOH, and -SO 3 H, (d) a fourth functional group (z) selected from: -H, -CH 3, -NR 4 R 5, -OH, -COOH and -SO 3 H, wherein: (R 4) and (R 5) are independently selected from: -H and hydrocarbyl groups comprising from 1 to 10 carbon atoms; and iii) exposing the thin film polyamide layer to nitrous acid; wherein the method is characterized by: at least one of the polar and non-polar solutions further comprises a tri-hydrocarbyl phosphate compound represented by Formula I: wherein R 1, R 2 and R 3 are independently selected from hydrogen and hydrocarbyl groups comprising from 1 to 10 carbon atoms, with the proviso that no more than one of R 1, R 2 and R 3 are hydrogen; and the non-polar solution further comprises an acid-containing monomer comprising a C 2 -C 20 hydrocarbon moiety substituted with at least one carboxylic acid functional group or salt thereof and at least one amine-reactive functional group selected from: acyl halide, sulfonyl halide and anhydride, wherein the acid-containing monomer is distinct from the polyfunctional acyl halide monomer. i) applying a polar solution comprising a polyfunctional amine monomer and a non-polar solution comprising a polyfunctional acyl halide monomer to a surface of a porous support and interfacially polymerizing the monomers to form a thin film polyamide layer; ii) treating the thin film polyamide layer with a polyfunctional arene compound comprising 1 or 2 benzene rings collectively substituted with the following four functional groups: (a) a first functional group (w) selected from: -NR 4 R 5 and -OH, (b) a second functional group (x) selected from: -NR 4 R 5, -OH, -COOH, and-SO 3 H, (c) a third functional group (y) selected from: -H, - NR 4 R 5, -OH, -COOH, and -SO 3 H, (d) a fourth functional group (z) selected from: -H, -CH 3, -NR 4 R 5, -OH, -COOH and -SO 3 H, wherein: (R 4) and (R 5) are independently selected from: -H and hydrocarbyl groups comprising from 1 to 10 carbon atoms; and (a) a first functional group (w) selected from: -NR 4 R 5 and -OH, (b) a second functional group (x) selected from: -NR 4 R 5, -OH, -COOH, and-SO 3 H, (c) a third functional group (y) selected from: -H, - NR 4 R 5, -OH, -COOH, and -SO 3 H, (d) a fourth functional group (z) selected from: -H, -CH 3, -NR 4 R 5, -OH, -COOH and -SO 3 H, wherein: (R 4) and (R 5) are independently selected from: -H and hydrocarbyl groups comprising from 1 to 10 carbon atoms; and iii) exposing the thin film polyamide layer to nitrous acid; at least one of the polar and non-polar solutions further comprises a tri-hydrocarbyl phosphate compound represented by Formula I: wherein R 1, R 2 and R 3 are independently selected from hydrogen and hydrocarbyl groups comprising from 1 to 10 carbon atoms, with the proviso that no more than one of R 1, R 2 and R 3 are hydrogen; and the non-polar solution further comprises an acid-containing monomer comprising a C 2 -C 20 hydrocarbon moiety substituted with at least one carboxylic acid functional group or salt thereof and at least one amine-reactive functional group selected from: acyl halide, sulfonyl halide and anhydride, wherein the acid-containing monomer is distinct from the polyfunctional acyl halide monomer.