The large differences in influent-water quality between the two countries are a consequence of differences in geology, precipitation patterns and the specific water sources used for smolt production. In Norway, surface water is the predominant influent-water source, with lake inlets constituting 88% and river inlets 12%. The Chilean water sources are more diverse, utilizing groundwater from deep wells (32%) and springs (40%) and also surface water from river inlets (28%). Most Norwegian sites have inlet-water quality that requires substantial increase in buffering capacity to obtain suitable pH and alkalinity for RAS systems (Fig. 2A and E). Chilean sites in general are almost an order of magnitude higher in Ca2+ and Mg2+ levels (Fig. 2C and D). At-site variability for many parameters is high in both countries. The presented data differ in the number of samples at each site (n = 1–12), and can therefore only be used to illustrate the presence of such variability, not to quantify variability or relate variability to season or other factors. This illustrates the need to monitor inlet-water over time to obtain reliable data on variability of critical parameters.