Biodiversity can increase the resistance and resilience of forest communities in the face of global change. To ensure proper management of forest ecosystems and water resources, it is thus crucial to understand how management decisions to maximize biodiversity may influence forest transpiration. Studies have found a positive relationship between biodiversity and vegetation transpiration. However, neutral, and negative associations have also been reported with contrasting results partially explained by soil types, soil moisture conditions, and forest types. The main objective of the meta-analysis was to evaluate the influence of tree diversity on forest transpiration and water use across climatic and environmental conditions. We selected 30 studies across 13 climatic regions that compared the transpiration of monocultures and mixed forests. We found that overall, there is a positive effect of tree diversity on forest transpiration at the stand scale. However, the positive effect of diversity on transpiration disappeared when trees experienced drier-than-normal conditions. Besides, we found that tree diversity had mixed effects (positive, negative, and neutral) on the transpiration of 33 different species. In conclusion, the influence of biodiversity on transpiration appears context dependent and this work helps improve our ability to transfer findings across space and time.