Rainwater harvesting and water conservation in commercial landscapes in Arizona - a case study

Rainwater harvesting (RWH) in arid and semiarid areas can conserve potable water by supplementing landscape irrigation. The City of Tucson established the first RWH ordinance in the nation in 2008, requiring commercial properties to capture rainwater so that 50% of their landscape irrigation needs can be fulfilled by RWH. The objectives of this study were to assess 20 properties subject to the RWH ordinance regarding irrigation practices, conservation of potable water, and compliance with the ordinance. The volume of irrigation applied at the 20 sites varied by year from 2015 to 2018. Monthly irrigation was not consistently matched to seasonal evapotranspiration demand or rainfall. Averaged over a four-year period, the annual application of irrigation water was in compliance with the RWH ordinance for all except four sites. Averaged over a four-year period, fifteen sites used only 0.4% to 37% of the allocated annual irrigation stipulated in the landscape water budget.