Expanding Disk Rain Sensor Performance and Potential Irrigation Water Savings

Rain sensors (RSs) appear to be a useful tool for water conservation at a relatively low cost. However, little evidence related to RS performance and/or reliability exists. The objectives of this experiment were to: (1) evaluate two RS types with respect to the following: Accuracy of their set point, number of irrigation cycles bypassed, and duration in bypass mode; (2) quantify the amount of water that RSs could save; and (3) estimate their payback period. Mini-click (MC) and wireless rain-click (WL) rain sensor models were monitored. For the WL treatment, the dry-out ventilation windows were set half open, and for the MC treatments, rainfall set points of 3, 13, and $25\mathrm{mm}$ were established. On average, all treatments responded close to their set points with the WL, $3\mathrm{mm}$ MC, $13\mathrm{mm}$ MC, and $25\mathrm{mm}$ MC treatments averaging 1.4, 3.4, 10.0, and $24.5\mathrm{mm}$ , respectively. However, some replicates showed variable behavior. The number of times that these sensors shut off irrigation (81, 43, 30, and 8 times, respectively) was inversely proportional to the magnitude of their set point, with potential water savings following a similar trend. Where water costs exceed $0.53 per cubic meter ($2.00 per thousand gallons), the payback period is less than a year for WL and MCs set at $13\mathrm{mm}$ or less.