Chemistry of injected water can modify the wettability behaviour of carbonate reservoirs. Wettability modification towards more water-wet reservoir rocks results in increased oil production. Smart water production by selective ionic water content is a major developing area in current enhanced oil recovery (EOR). Technical limitations for smart water production for EOR using seawater as feed for membranes are described in this paper. Desired characteristics of smart water for injection into carbonate reservoirs are low Na+ and Cl- and high divalent ion concentrations. Wettability alteration by smart water occurs due to symbiotic behaviour of Ca2+, SO4 2- and Mg2+ ions and the carboxylic material of the reservoir rock surface. Nano-filtration (NF) and Reverse Osmosis (RO) membranes were used for ion separation experiments. Retentate from NF contains the main constituents of smart water. Membrane performance was evaluated in terms of rejection under varying feed compositions and pressures. An analysis of general approaches for water injection processes from seawater is discussed. This paper delivers an economic framework for evaluation of the water injection process by including major technical and economical elements. Main criteria considered in this research were how to decrease monovalent ion rejection. This was achieved by increasing divalent ion concentration by spiking feed water with selected chemicals. Results showed that a decrease in retention of monovalent ions was achieved by increasing multivalent ion concentration in the feed. A challenge of smart water production is the high dissolved solids content (TDS) in retentate from NF. Three options to dilute the retentate were evaluated; i.e., combinations of NF and RO, MSFD and fresh water. The most feasible process is a combination of NF and RO, with an energy consumption of 3.8 kWh/m3.