This publication presents the outcome of an IAEA coordinated research project and provides research findings and isotopic methodologies to quantify the soil evaporation component of water losses and determine the transpiration efficiency for several important crop species under a variety of environments. The TECDOC also presents a simple, fast and portable vacuum distillation apparatus for extraction water from soil and plant samples for isotopic analyses for the separation of soil evaporation, which helped to reduce the bottleneck in sample throughput for many soil water and hydrology studies.