Device for the direct estimation of evapotranspiration. Typically it comprises a vegetated block of soil of volume 0.5–1 m3, to which the amount of water added is known, and from which the amount lost as runoff or percolation may be measured. Recording the changing weight of the soil-vegetation system (keeping vegetation change due to growth static or monitored) reveals the amount of water retained by the system, and thus, by difference, the amount lost as evapotranspiration. For geographic comparisons an easily standardized, short, grass vegetation cover is used. For water-budget experiments, vegetation cover may be varied to simulate different crop types or semi-natural communities.