A simple method for determining desalination requirements in semi-arid regions is described and illustrated by a case study for the region between the Mediterranean Sea and the Jordan River. Analysis of a 78 year series of regional recharge values derived from rainfall measurements showed a large inter-annual variability with no evidence of a significant trend. The fitted gamma distribution was used to estimate the probabilities of the annual regional water consumption exceeding recharge leading to a need for desalination. Near-future water consumption was estimated from current trends and used to assess the probabilities of regional water deficits arising and the volume of desalination required. The economic and environmental costs of using desalinated sea water and rain-fed ground water are briefly reviewed and the need for a stochastic approach to planning desalination requirements in semi-arid zones is emphasized. (C) 2014 Elsevier B.V. All rights reserved.