How much water does an oak transpire?

Oaks do move water from roots to leaves and lose it through transpiration, but the “up to 7 tonnes per day” figure could not be verified with reliable measurement evidence. Data for particular species and conditions show highly variable rates: one field study of a Portuguese oak measured a maximum of about 3 mm of water per day over the crown-projected area, while another reference gives about 227 litres per day for a mature oak. The amount depends on the tree, weather, and water availability.