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The process of pollution risk assessment requires the assimilation of data that are spatially variable in nature, making geographical information systems (GIS) an ideal tool for such assessments. Over half of Britain's drinking water is obtained from surface water abstractions, many of which are situated in upland areas. In order to optimise the quality of abstracted waters it is important to assess the possible risks of pollution upstream from the point of abstraction. This paper describes the use of the PC-based WINGS™ and MapInfo Professional™ geographical information systems in the evolution of a risk assessment methodology to assess catchment risk. The work illustrates how such technology can assist in environmental decision-making to optimise the quality of drinking water supplies and enhance treatment efficiencies. Examples are given showing how raster and vector-based data can be used within a GIS framework to produce maps indicating areas of potential hazard to water quality, and coupled with existing models to predict and quantify risk frequency and impact. GIS techniques are further utilised in the formulation of a raw water monitoring programme to assist in intake operation and land-use planning in the catchment. The availability of suitable digital data was found to be variable, and some problems encountered in their integration and implementation within the system framework were resolved. Comment is given on the suitability and relative performance of the two software packages in the assessment of catchment risk. The work was carried out on a medium specification desktop PC, and therefore has the potential to be utilised across the intranet of a large utility company.