<p>Ultrapure water (UPW) is one of the most important and critical requirements of Rankine cycle-based power plants. This research study presents an experimental case study of the replacement of the ion exchanger (IX) with a reverse osmosis-electrodeionization integrated system (RO-EDI) for ultrapure water production in a 62.4 MW cogeneration power plant. In this study, the water quality parameters produced through RO-EDI integration were evaluated for high-pressure (110 bar) boiler water quality requirements. The operational costs of both systems were compared to check the feasibility of the RO-EDI system, which has a slightly higher initial operational cost than the IX, where the feed water conductivity is less than 750 µS/cm. The operational costs of both systems are comparable: it is 1.8% higher for RO-EDI at lower raw water conductivity, but at peak raw water conductivity it increases by 1.1% for RO-IX. This comparison treatment indicates that both systems operate at a comparable overall operational cost of approximately US $ 0.16 per m³ of ultrapure water. At an initial feed water conductivity of 650 µS/cm, the RO-EDI process exhibited a slightly higher operating cost about US $ 0.03 per m³ than RO-IX. However, as feed water conductivity increased, the effective operating hours of the RO-IX system declined, leading to a rise in its unit treatment cost. At a conductivity level of 850 µS/cm, the operational cost of RO-IX exceeded that of RO-EDI by roughly US $ 0.0035 per m³. However, with an increase in conductivity above 750 µS/cm, the RO-IX operational cost increased compared to that of RO-EDI. The operational cost of the traditional IX method includes chemical and electricity costs, whereas in the case of RO-EDI there is only electricity cost.</p>