Food industry largely depends on water use for processing, cleaning and washing operations, and heat and mass transfer (boilers, cooling circuits, refrigeration…). In the context of increasing water scarcity and price, the French program ANR MINIMEAU (ANR-17-CE10-0015, https://minimeau.fr) developed tools to help factories minimize water consumption by implementing the reuse (without treatment) and recycling (after treatment) of wastewater. Amongst them, a new filtration module was developed in the ProSimPlus software (ProSim SA, France) for the simulation of reverse osmosis (RO) and tight nanofiltration processes, which led to revisit the design rules of multi-stage systems. It is based on the solution-diffusion model, considers concentration polarization and osmotic effects, and requires the preliminary determination of the membrane permeability: for water and for the targeted pollution parameters to remove from the effluent. Pilot-scale experiments were run to obtain the required data for a previously selected RO membrane (ESPA4-LD from Hydranautics, Nitto Denko) and two process water streams of a French vegetable plant, the organic contaminants of which were studied: COD, total nitrogen, sugars (sucrose, glucose, fructose) and organic acids (lactic and acetic) (Garnier et al. 2020; Garnier et al. 2022). Considering the effluent flowrate, the desired range for the conversion rate and the hydraulic requirements, simple rules were used to develop different design options for multi-stage systems. Their treatment performances could be calculated and compared using the ProSimPlus software, highlighting key parameters for the design.