Condensation phenomenon in free expansion plumes has been observed and studied in the last several decades. Recently, the direct simulation Monte Carlo (DSMC), a kinetic method, was expanded to include the simulation of homogeneous condensation in the free expansion of primarily argon plumes. To extend our studies of homogeneous condensation to small, polar molecules, such as water, produced in the combustion products of chemical propellants, accurate microscopic cluster model need to be developed. In this work, the molecular dynamics (MD) method is used to calculate the water cluster sizes, clustermonomer collision and sticking probabilities necessary for the study of water homogeneous condensation in a plume expanding to low pressure, space conditions. The molecular dynamics results are integrated into a DSMC simulation and the simulated Rayleigh scattering intensities are compared with experimental data to test the models and numerical results.