Forest planners provide decision makers with a wide array of information for making strategic decisions across broad landscapes. While wildlife and fisheries habitat concerns have strongly influenced the management of national forests over the past decade, the quantity and quality of water is now becoming one of the top priorities. Competition for downstream use of water and instream flows required to maintain or improve aquatic habitat conditions, suggest that the US Forest Service considers water yields to be an important measure of output from new forest plans. While significant research has been focused on the development of hydrologic models, the challenge is to now apply what has been learned to policy analysis. And when assessing a resource that moves across a landscape, a multi-ownership perspective may be needed. This paper describes the main aspects of water yield models and thoughts regarding the challenges planners and policy makers may face when integrating them with forest planning models.