Our article deals with the possibilities to treat seawater using commercial nanofiltration polyamide membranes, denoted NF70 and NF 200, in order to elaborate usable salty aqueous solutions (from high concentrated solutions with total salinity around 70 g/L to isotonic solutions with total salinity in the range of 4 g/L). A theoretical part concerned a hydrodynamical model of mass transfer. This very simple model based on the permeate salt concentrations (using conductivity measurements) vs. the reverse of the permeate flux has been validated for the first time for seawater. This very interesting approach is able to quantify separately both parts of the mass transfer occurring in NF — convection and hydration-diffusion. This fundamental approach was developed in order to contribute to a better understanding of the selectivities observed between monovalent and divalent ions in NF operation. The experiments were conducted in Biarritz (south-west France) under coal pre-filter seawater, just after the Prestige's oil pollution, in order to elaborate personal body washing solutions using NF permeates. Concerning the concentrates we have contributed to the elaboration of hypertonic salty solutions for thalassotherapy centers or home bath applications. Indeed the possibilities of NF in reducing the overall salinity of seawater leads the way to potential applications in the field of human health (e.g., preparation of nasal sprays, medical dietetics, hot mineral springs). Furthermore our investigations conducted in the holy place of the Biarritz Seawater Museum have contributed to discovery of the possibilities of NF concentrates for coral growth studies.