Water atomization can be used to produce wide range of particle size, shape and particle size distribution of metal powder efficiently by varying operating variables which include design parameters, process parameters and thermophysical properties of metal and water. Liquid copper was water atomized in a laboratory fabricated atomizer. Few experiments were conducted to produce copper powder by varying water jet pressure. In the present work, mathematical model was formulated to propose a relationship between particle size of copper powder and operating variables. Proposed mathematical model is developed to predict particle size affected by different parameters and validated with experimental results. 3-D surface response was analyzed by varying water pressure and apex angle. (C) 2013 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.