Many correlations have been developed between water split (ratio of water reporting through underflow and overflow) and process as well as design variables in a hydrocyclone. However, majority of them use cone ratio (ratio of spigot and vortex finder diameter) as one of the variables. In this article, it is explained why the use of cone ratio as a model parameter may sometimes be misleading. An attempt has, therefore, been made to develop an improved correlation to predict water split in a hydrocyclone using spigot diameter and vortex finder diameter as individual variables. Feed pressure has also been used as a model parameter. The model has been developed based on regression analyses of systematic data generated and has been validated with random experimental data. (c) 2005 Elsevier Ltd. All rights reserved.