Carboxylated polysulfone (CPS), poly (1,4-phenylene ether ethersulfone) (PPEES), membranes were prepared and used for the separation of NaCl and $CaCl_2$, in efficient way with less energy consumption. In this work, nanofiltration and reverse osmosis membranes were employed to the salt rejection behavior of the different salt solutions. The influence of applied pressure (1-12 bar), on the membrane performance was assessed. In CM series of membranes, $CM_1$ showed maximum of 97% water uptake and 36% water swelling, whereas, $CM_4$ showed 75% water uptake and 28% water swelling. In RCM series, $RCM_1$ showed 85% water uptake and 32% water swelling whereas, in $RCM_4$ it was 68% for water uptake and 20% for water swelling. Conclusively reverse osmosis membranes gave better rejection whereas nanofiltration membrane showed enhanced flux. CM1 showed 58% of rejection with 12 L/($m^2$ h) flux and $RCM_1$ showed 55% of rejection with 15 L/($m^2$ h) flux for 0.1 wt.% NaCl solution. Whereas, in 0.1 wt.% $CaCl_2$ solution, membrane $CM_1$ showed 78% of rejection with 12 L/($m^2$ h) flux and $RCM_1$ showed 63% rejection with flux of 9 L/($m^2$ h).