Correctly programming the controller is necessary to achieve water savings. Many controllers have default settings to water plants at levels sufficient to meet 100 percent of a plant’s theoretical water needs (i.e., 100 percent ET). These theoretical water needs have been calculated based on a single crop type in a single microclimate, where the focus was on maximizing yield.
Landscape plants, however, should be treated differently than crops because a landscape typically reflects a mixture of plant species with varying vegetation density and microclimates, and most plants will require less than their theoretical water needs to maintain proper health and appearance. Thus, a WBIC can be adjusted to better reflect the plant’s water needs.
Providing the correct programming inputs on these controllers using the site-specific parameters is imperative to achieve an appropriate watering level. The percent adjust, or water budget, feature present on all WaterSense labeled controllers is a simple way to adjust the amount of water that is applied to the landscape. This feature can be a simple dial or button to allow more or less water to be applied to a specific irrigation zone.
Source: Weather-Based Irrigation Controller Mini Report (https://www.epa.gov/sites/production/files/2017-01/documents/ws-products-minireport-irrigation-controllers.pdf)