Water accounting is becoming critical globally, and balancing consumptive water demands with environmental water requirements is especially difficult in arid and semiarid regions. Within the Murray-Darling Basin (MDB) in Australia, riparian water use has not been assessed across broad scales. An existing U.S. riparian ecosystem evapotranspiration (ET) algorithm was applied to the MDB river systems to help quantify environmental water needs over a wide range of niche conditions. Ground-based sap flow ET was correlated with remotely sensed predictions of ET to provide a method to scale annual rates of water consumption by riparian vegetation over entire irrigation districts. Sap flux was measured at nine locations on the Murrumbidgee River between July 2011 and June 2012. Remotely sensed ET was calculated using a combination of local meteorological estimates of potential ET (ETo) and rainfall, and MODIS EVI from selected 250-m resolution pixels. The sap flow data correlated well with MODIS EVI and water use was within the range of expected values. We conclude that the algorithm developed for U.S. arid land crops and riparian plants is applicable to this region of Australia. Future work includes the development of an adjusted algorithm using these sap flow validated results.