A dual-element multipoint optical fibre sensor system capable of detecting ethanol in water supplies is reported. The sensor system utilises a U-bend configuration for each sensor element in order to maximise the sensitivity of the system and is interrogated using a technique known as optical time domain reflectometry, as this method is capable of detecting attenuation over distance. Analysis of the data arising from the sensor system is performed using artificial neural network (ANN) pattern recognition techniques, coupled with Fourier transform-based signal processing. The signal processing techniques are applied to the obtained sensor system data, prior to the ANN analysis, with the aim of reducing the computational resources required by the implemented ANN in software. (C) 2004 Elsevier B.V. All rights reserved.