A first stream of an aqueous solution flows through an upstream desalination or nanofiltration system. A second stream of the aqueous solution is mixed with the diluate output from the upstream desalination system or with the diluate or concentrate output from the upstream nanofiltration system with a flow ratio of the second stream of the aqueous solution to the feed stream of 0.63. A liquid composition flows into the concentrate channels of an electrically driven separation apparatus, while the feed stream flows into at least the diluate channels at a ratio of 0.3 to 0.81 to the flow of the liquid composition. An applied voltage selectively draws monovalent ions from the feed stream in the diluate channels through the monovalent-selective ion exchange membranes into the concentrate channels to produce a treated diluate having a sodium chloride ratio (SCR)