Among desalination processes, the use of seawater reverse osmosis (RO) increased in the last few years. Pretreatment before RO is an essential step to guarantee the success of the whole process. Indeed, biofouling of RO membranes usually occurs when bacteria, their potential nutrients such as dissolved organic carbon (DOC), and precursors such as transparent exopolymer particles (TEP), present in natural seawater, are not successfully removed by the pretreatments. Consequently, in this study, coupling granular activated carbon (GAC) adsorption and ultrafiltration as a pretreatment before RO is proposed on a community-scale desalination plant. This plant was designed to produce 5 m3 d−1 of desalinated water and was continuously operated on site with natural seawater. The two-month study of this desalination plant showed that the GAC bed could highly reduce by 20–80% DOC concentration. Ultrafiltration could retain most of TEP and bacteria before RO. RO parameters were stable meaning that no biofouling was detected. Therefore, the need of chemicals was close to zero and the RO recovery rate reached 70% enabling RO energy consumption to reach 4 kWh m−3. The results showed the potential of process intensification in such desalination plants.