A simplified climate change impact assessment tool (SCIAT) has been developed to address the specific needs of the water industry and provides a tool to translate climate change projections into ‘real world’ impacts. Its application is demonstrated in this study to assess the impacts of climate change on the reservoir water quality and water treatment plant (WTP) operations at Grafham Water in the east of England. The primary aim is to provide WTP operators with knowledge of the potential impacts and associated probabilities of occurrence of climate change, enabling them to make informed, risk-based adaptation and planning decisions. Using a series of coupled hydrological and water-quality models, it is likely that there will be a decline in average reservoir water quality. Climate change will also have an impact on WTP operations, but these will be manageable within the current operational parameters.