To date, key water–energy connections have not been systematically quantified. Nor has their potential for contributing to greenhouse gas mitigation been evaluated. Lack of knowledge of these links, particularly within cities, is viewed as a major limitation to energy-sensitive urban water management and integrated urban design. This paper fills part of this void. The key contribution is a new conceptual model coupled with a systematic review of the connections of influence. Drawing on Australian and international data, the results provide a structured estimate of water-related energy use and associated emissions in a hypothetical city of 1,000,000 people. This demonstrates that water-related energy use accounts for 13% of total electricity and 18% of the natural gas used by the population in the average case. This represents 9% of the total primary energy demand within Australia or 8% of total national territorial greenhouse gas emissions. Residential, industrial and commercial water-related energy use constitutes 86% of water-related greenhouse gas emissions. We conclude that urban water is a significant and overlooked lever that could significantly influence urban energy consumption.