Estimating the value of changes in water quality requires the definition of biophysical features that link changes in ecosystems to changes in social systems. Those linking features must be interpretable to people and serve as effective ecological indicators. This work defines a linking feature that is appropriate for capturing existence values in a forthcoming national stated preference survey of Clean Water Act regulations. Further, we modeled and spatially predicted this feature to account for the dependence of survey respondents’ preference on baseline aquatic conditions near them. We outline steps to provide insights on the mechanisms that will aid in forecasting changes in the linking feature in responses to candidate policy options.