Increasing water scarcity, higher evapotranspiration rates and reduced rainfall have generated a need for fundamental improvements in irrigation water use efficiency. Evaporation is a significant component of the total evapotranspiration (ET) and high evaporation losses reduce the amount of available water for transpiration, resulting in reduced plant water availability and hence increased irrigation. In order to increase transpiration relative to evaporation and with enhanced pressure on water resources, a reduction in evaporative losses would lead to improved water use efficiency. In order to access the magnitude of soil evaporation losses in semi-arid vineyards and its effects on water use efficiency extensive field trials were carried out to quantify soil evaporation losses. The magnitude of soil evaporation was determined using direct and indirect measurements on a bare soil and in a commercial vineyard.