Access to clean water is a major global issue. Saline and wastewater can be returned to high quality freshwater through reverse osmosis (RO) desalination. The main operational challenge for this process is scaling and biofouling, which decreases RO water recovery and increases energy- and chemical consumption. Conventional RO systems are operated in continuous mode with constant brine salinity. In such systems, fouling organisms adapt and form biofilms on the RO membrane. Operating RO systems in batch mode with fluctuating salinity and intermittent brine discharge can reduce water and energy consumption. However, few such installations exist, and it is not known if batch RO operation can be used to eradicate biofouling. We hypothesize that, with appropriate controls, batch operation of RO will minimize biofouling as alternating salinity hinders the biofilm-forming microorganism´s ability to adapt and proliferate. The aim of BE-SALT is to provide mechanistic insight into biofouling and scaling under fluctuating salt stress implement this knowledge into design and optimization of sensor-based operation of batch RO systems and reduce operational cost (water, energy, chemicals) by >15% compared to continuous RO systems, while enabling high water recovery rates (>75 %) demonstrate the concept in pilot scale and at an end-user Our vision is to lead the way for process design and water/energy efficient operation of RO systems for clean water production.