The solubility of water in the organic solutions, containing hydrocarbons, has traditionally been modeled by using empirical correlations. In this communication, an extended Setschenow model is proposed for predicting the organic solubility of water in a 5-100% tri-n-butyl phosphate/diluent-nitric acid-water biphasic system at 298.2 K. The literature data on water solubility were correlated to aqueous acid concentration and diluent concentration in the solvents. The proposed model was extended for temperature dependency of the solubility.