Rapid population growth in arid regions of the western US is placing increased demand on water resources. Variability in precipitation and common occurrence of drought have promoted scrutiny of water use in urban lawns and gardens. However, few reliable measurements of water use of these landscapes exist. Quantifying the amount of water used vs. required by landscapes such as turfgrass would allow significant water conservation. Evapotranspiration (ET) is affected by biophysical factors such as: available energy, turbulent mixing, saturation deficit, soil water, and stomatal conductance. In order to simulate the water use by turfgrass, the relative importance of these processes must be determined for this environment. This study measures ET rates for Kentucky bluegrass using eddy covariance techniques, to quantify water use under various conditions. The results are combined with a coupled form of the Penman-Monteith Equation to determine which biophysical factors affect the ET rate under various atmospheric conditions, especially the advection of heat and saturation deficit from the regional atmosphere. In addition, changes in ET and other properties of the vegetation were monitored during a period of reduced irrigation or dry-down. These results will help determine the amount of water such landscapes actually need.