A coolant mixture including water and at least one of the compounds chosen from 1-methoxy-2-propanol and 1-ethoxy-2-propanol in the proportions of the corresponding azeotrope or in near-azeotropic proportions. Such a mixture can be used as a heat-transfer fluid in a heat-exchange device, which can be incorporated into an aircraft or spacecraft. A method for obtaining a mixture by fractional distillation is also disclosed.