Poly(sulfone-co-amide) polymer was synthesized by a low temperature solution polycondensation technique from benzene 1,3 dicarboxylic acid chloride (isophthaloyl chloride), benzene 1,4 dicarboxylic acid chloride [terephthaloyl chloride (TPC)], and bis[4-amino phenyl] sulfone, i.e., (4,4'-diamino diphenyl sulfone) as monomers using N,N dimethyl acetamide (DMAc) as solvent cum acid acceptor. Casting solutions using various combinations of DMAc and acetone as solvent and LiCl and LiNO3 as additives were prepared. Wet phase inversion membranes were prepared from them at ambient temperature (25degreesC) using demineralized water (DMW) or aqueous sodium dodecyl sulfate (SDS) as coagulation media. Solute rejections of the membranes increased and solvent flux decreased with increasing proportion of acetone and decreasing DMAc content in the casting solution. Use of 1% and 2% aqueous SDS solution as gelling media improved the flux of the membranes significantly. Evaporation of solvent at room temperature prior to gelling, in certain cases, led to high solute rejecting membranes. By the proper combination of casting solution composition, evaporation time, and gelling medium, it was possible to make a range of NF membranes and also high solute rejecting brackish water RO membranes from the single polymer. More importantly, use of a significant amount of acetone in the casting solution enabled us to make high solute rejecting integrally skinned asymmetric membranes simply by evaporation of solvent followed by coagulation in a proper medium, all at ambient temperature. The membranes do not need any other treatment before use.