Snowmaking is the main adaptation of winter tourism to climate change. It involves the use of large amounts of water, which can lead to conflicts with other human uses and ecosystem needs. The number of reservoirs used to support snowmaking is increasing, as they allow production capacity to be increased, the best cold periods to be selected and snowmaking to be more efficient. The French Association of Ski Lift Operators claims that reservoirs reduce water withdrawals during low flow periods in winter, which can be considered as eco-efficiency. Using a dataset of 35 ski resorts over 9 seasons, we show that reservoirs significantly increase withdrawals, both on an annual scale and during low flow periods. This effect is an illustration of the so-called rebound effect, where a technology that promises greater efficiency in resource use actually leads to greater absolute resource use. A one per cent increase in reservoir storage capacity would lead to a 0.68% increase in annual snowmaking withdrawals and a 0.72% increase in low flow withdrawals, ceteris paribus. This research informs ongoing discussions to ensure that current socio-economic decisions do not lead to future water use conflicts in mountain socio-ecological systems.