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Sioux Falls, SD is in the climate transition zone between the humid Midwest and semiarid Great Plains. Outdoor water use in Sioux Falls accounts for about half of the daily demand during the summer. To reduce the outdoor water demand, ET-based landscape irrigation control was compared to time-based control. For the 2009 irrigation season, 36 volunteer homeowners were divided into three treatments- replacement of 100% of the irrigation requirement (estimated ET minus rainfall), replacement of 70% of irrigation requirement, and traditional time-based control (the control treatment). Homes in the time-based and 70% treatments reduced their outdoor water application during 2009 compared to 2008. The reductions of the ratio of outdoor water application to irrigation requirement were 0.22 and 0.15 for the 80% and time-based treatments, respectively. Homes in the 100% treatment increased their water application slightly during 2009 (the change of the ratio of outdoor water application to irrigation requirement was 0.25). However, there were no statistical differences among the treatments. After one season of use, the ET-based controllers show promise for reducing outdoor (landscape irrigation) water application but the reductions were not significant.