Water activity measurements have been carried out on the aqueous solutions of both tri-potassium citrate (K(3)Cit) and polypropylene oxide (PPO) 400 + K(3)Cit over a range of temperatures at atmospheric pressure. The data obtained is used to calculate the vapor pressure as a function of temperature and concentration. The effect of temperature on the constant water activity lines of aqueous PPO + K(3)Cit systems has been studied and it was found that, at higher temperatures the higher concentration of polymer is in equilibrium with a certain concentration of the salt. Also it was found that the vapor pressure depression for an aqueous PPO + K(3)Cit system is more than the sum of those for the corresponding binary solutions. The experimental water activities have been correlated successfully with the segment-based local composition Wilson model. The agreement between the correlation and the experimental data is good. (c) 2007 Elsevier B.V. All rights reserved.