The solubility of water in molten aliphatic polyamides (nylons) of high degrees of polymerization at conditions of subatmospheric water partial pressure and high temperature (225 to 300degreesC) has been modeled. A simple, serni-empirical model based on Flory-Huggins theory was fit to the available literature data for nylons 6, 66, 610 and 11 and to new experimental data for nylon 612. The model contains only two fitted parameters, and is able to adequately describe the available data for the effects of temperature and nylon type on the water concentration in the melt at various water partial pressures.