Many features of the Martian landscape are thought to have been formed by liquid water flow. However, several lines of evidence suggest that mean global temperatures on early Mars were well below the freezing point of pure water. Here, the modelling of freezing and evaporation of Martian fluids with a chemical composition resulting from the weathering of basaltsas reflected in the chemical compositions found at Mars landing sitessuggests that a significant fraction would remain in the liquid state at temperatures well below 273 K.