This article is an extended summary of the report prepared by the Process Water Subgroup of the European Hygienic Engineering & Design Group (EHEDG). It is the 23rd in the series of EHEDG summaries published in TIFS. Copies of the full report (EHEDG Doc. 24, August 2002) prepared by A.M. van Buren (Chairman), J.A. Milligan, H.M.J. van Eijk, J. O'Brien, S.D. Pannell, D. Lawrence, R. Hopman, W.G.J.M. van Tongeren, are available from CCFRA at pubs@camden.co.uk Information about EHEDG can be found on the website at www.ehedg.org It is strongly recommended that for application in the field, operators in the food industry should read the guidelines in its entirety, to ensure a holistic approach to legionella control. (C) 2002 Elsevier Science Ltd. All rights reserved.