Models for cell dehydration during a cryopreservation protocol are usually based on the hypothesis of id a dilute solution. The strong electrolyte character of NaCl makes us revisit these models. The case of nonideal solution is analyzed by computing the dehydration curves without this additional hypothesis. The conclusion is that, in general, while the application of the ideal dilute solution hypothesis is convenient in many cases, for some specific cooling rates there exist important differences in the degree of dehydration predicted by these two models in the studied cases of mouse sperm and hepatocyte. It is shown how this finding has relevant implications for the design and optimization of cryopreservation protocols.