Crossflow filtration is used from small laboratory-scale systems carrying out research, to large-scale facilities producing food and water, Many aspects of the technology are now well established, However, scaling up from data sheets to large-scale plants is fraught with dangers, because of the lack of knowledge about the real challenge and its variability, In this article Dr Peter Cardew and M Byrne of NWW Acumem Ltd, UK highlight the benefits of carrying out laboratory and field-testing, and their impact on scale, Some effluent applications are used to emphasise the important benefits in carrying out such studies.