The present work describes the design and analysis of a compact and modular wave-powered desalination (WPD) system. The design of the unit is influenced by the United States Department of Energy (DOE) Waves to Water competition rules. The system consists of a flap-type wave surge converter that converts wave energy into hydraulic piston force through a double-acting cylinder working as a power take-off (PTO) device. The dimensions of the flap are determined through frequency domain analysis under different sea states and the required discharge of desalinated water. Further, the whole system, including the reverse osmosis (RO) module, is modeled using WEC-Sim (an open-source code) and Simscape/SimHydraulics toolbox in MATLAB. The analysis of the system under six different sea states shows encouraging results for freshwater production. Considering the sea states studied here, the designed system can generate more than 50 bar pressure of the seawater feed discharge and produce up to 100 L/h of freshwater with TDS less than 500 mg/L. It was also observed that the use of an accumulator reduces the fluctuation in feed flow and feed pressure at the inlet of the RO module, resulting in improved system efficiency.