The shortage of water in Mediterranean hydrographic basins of the Iberian Peninsula has led to the development of desalination plants which use reverse osmosis to supply drinking water. This has caused a variation of the organoleptic characteristics in the water supply which have led to the appearance of medicinal taste and, to a lesser extent, odour. The aim of this study was to determine the substances that have led to this state of affairs. After analytical determinations by SPME-GC/MS, it was found that bromophenols (2-bromophenol, 2,4-and 2,6-dibromophenol) are responsible and their sensory threshold being in some cases lower than 10 ng L-1. The chlorination (5 mg CI L-1) of the desalinated water with bromide levels (0.3 to 0.8 mg L-1) leads to the development of bromophenols that even after one month have maintained high levels of concentration. This fact does not occur in the case of continental waters with low bromide content (0.1 mg L-1) when they are treated in the same way. (C) 2012 Elsevier B.V. All rights reserved.