The substitution of volatile hydrocarbons by the use of water as blowing agent in the synthesis of expandable polystyrene particles has been studied in the last decades. In this work, an investigation was made of the influence of experimental parameters on the incorporation of water in the synthesis of water-expandable polystyrene. The synthesis procedure was based on a two-step polymerization, namely a water dispersion stage and a suspension polymerization stage. The use of a surfactant with a low HLB value resulted in a more stable water-in-oil system and smaller water droplets. The type of impeller used during the dispersion of the water in the monomer phase also influenced the formation of water droplets. In addition, the diameter of the droplets was strongly influenced by the duration of the water dispersion phase. Results suggested that these parameters can be used to control the characteristics of the water droplets formed inside the polystyrene particles.