Economic Research Institute Study paper
Utah State University
I begin with a strong assertion. There is no unused water! Whatever water is used for, for merely looking at it, to using it for a duck marshland, to drinking, there is a value placed on it by someone. This leads to the corollary that for each change in a particular projected or present use there is something that must be given up.
Andersen, Jay C., "Environmental and Recreational Considerations" (1979). Economic Research Institute Study Papers. Paper 380.