Many rural landowners within the Western United States do not have access to a secure water supply provided by a major dam or an irrigation district. Such water users must rely instead on groundwater pumping and/or seasonal water flows from tributaries. Some of these agricultural producers choose to store winter stream flows from tributaries within onsite reservoirs to secure their spring/summer water needs. However, regulatory agencies have increased restrictions on surface water storage and diversions to improve instream flows for endangered salmon, thus reducing water security for many landowners not located along the main stem. The majority of salmon habitat is within the tributaries located throughout a watershed. Most research regarding instream flows and water management, however, has focused on the main stem portion of a watershed and not on its tributaries. Such a focus ignores the important fact that most landowners are found off the main stem. Consequently, effective water management policies aimed at improving water security and salmon survivorship must focus on the main stem and the tributaries within a watershed. Our current research focuses on both of these critical areas. We Develop a spatially explicit economic model to analyze the demand for additional onsite storage with and without the existing regulatory restrictions. Using this model, we are able to determine which landowners have unmet demands for onsite storage versus those who prefer to pump groundwater, and thus would not request an appropriative water right for storage, even in the absence of a policy restriction.