An efficient market implies that potential gains from trade are fully captured. Achieving this requires a well-functioning market where prices reflect all available information. In the case of water rights markets, this implies that the permanent water rights transfer price reflects the sum of discounted returns to this asset (i.e., the lease price), the market interest rate, and a risk premium that reflects potential future water scarcity. The purpose of this study is to assess the efficiency of western U.S. water rights markets by utilizing the asset pricing model to measure how well prices reflect long-run returns to permanent water rights.