Dielectric relaxation measurements are reported over a frequency range from 10(-1) to 10(9) Hz as a function of exposure time for an epoxy resin-carbon fibre composite, ageing at 60 degrees C in water. Investigation of the nature of the dipole relaxation of the water molecules, indicates the nature of their interaction with the polymer matrix. Analysis of the dielectric relaxation spectra allow identification of processes that can be attributed to 'free' and 'bonded' water, water in micro-cracking, located in carbon fibre disbonds and plasticizing the polymer matrix. identification of the various types of location in which water exists was aided by use of the N-g factor from the Kirkwood-Frolich equation, which describes the constraints on free dipole ration nature imposed by the environment in which it is located. These data indicate the power of the dielectric technique for quantitative analysis of water ingress into epoxy composites. (c) 2004 Elsevier Ltd. All rights reserved.