Water supply and allocation is a problem that has plagued the West for most of its history. Water marketing, a greater emphasis on conservation, and surface water augmentation projects are all methods that have been used to address the problem. Another approach that has been around for quite some time but has been pushed to the forefront in recent years is the idea of conjunctive use management. In its broadest sense, conjunctive use management is simply linking surface and groundwater together and managing them as a common water supply pool. Rather than having one set of groundwater users and one set of surface water users, all are bound together by the need for more water. By doing so, excess surface water can be stored beneath the ground during wet times, and these same users can draw on the underground supply during times of drought. Similarly, the storage will increase the amount of water available underground so that overdraft conditions are diminished. In theory, this means that there will be an overall gain in the amount of water available for all users and that supplies can be managed on a more sustainable basis. In practice, Wiliam Blomquist, Edella Schlager, and Tanya Heikkila point out, existing institutions play a major role in determining the push for conjunctive use management and the form that it takes.

The emphasis on institutions is the focus of the book that makes this work appealing to a broad range of political scientists. While conjunctive use is the central theme of Common Water, Diverging Streams, water policy ends up being simply a vehicle that is used to explain public policy and public administration, and the role that institutions play in both.

The book is structured in three parts—”Common Waters: Managing Surface Water and Groundwater Resources Together,” “How Institutions Matter: Institutions and Conjunctive Management in California, Arizona, and Colorado,” and “Institutions and Policy Change: Analysis and Recommendations.” The strength of the book is found in the first two parts. In Part I, the authors do an outstanding job of describing the whole practice of conjunctive use management—from the different forms it might take to a range of alternatives for storing water below ground. Given the geology of a given area, water storage may not be as simple as allowing water to wash over an aquifer with the expectation that the water will sink in. Conjunctive management often requires expensive items, such as injection wells, to move surface water underground. They also point out a number of obstacles that may hinder states in their efforts to engage in conjunctive use management. The obstacles include, but are not limited to, existing water law, a lack of statewide leadership, and a lack of trust among water organizations (p. 14).

Part II centers around three case studies in conjunctive use and the relationship between institutions and management. In their discussion of California, Arizona, and Colorado, the authors are very thorough in their treatment of each state's physical setting, current institutional arrangements (including surface and groundwater law), and the emergence of conjunctive use. They are convincing in their demonstration of how the institutional arrangements largely dictated the shape and form that conjunctive use took in each particular state, which reinforces the book's primary claim. That said, the book does have some weaknesses.

One is left to wonder why Blomquist, Schlager, and Heikkila chose to focus on these three states to the exclusion of other western states engaged in conjunctive use. The authors claim that “without question, differences among the states result partly from physical and historical distinctions, but to a greater degree they illustrate how institutions matter” (p. 115). While they do a wonderful job of demonstrating how institutions have played a role in each individual state, for example the leverage wielded by the Central Arizona Water Conservation District, their use of only three states does not allow them to make the interstate connections that they do. While the authors do attempt to discuss methodology and state selection in an appendix entitled “The Three States: Why We Chose Them and What We Did,” the add-on comes across as an attempt at pleasing press reviewers, rather than something that truly gets to the heart of the matter—a wider range of states may have led to different findings. There is simply nothing to explain why other states, such as Nevada, which is facing even greater growth with similar water problems, are not included in the study.

Another weakness is that not enough emphasis is placed on politics and entrenched interests. While such institutions as laws, existing policies, and agencies/organizations clearly matter, so too do the interests that often drive these institutions. Laws, policies, and even organizations can change if external pressure is strong enough. The authors themselves discuss the decentralized nature of water management as being a tradition in California (pp. 53, 64, 67, 72). It is the entrenched local interests and those who benefit from the system that continue to push for this institutional arrangement—if enough new users were to push for a more centralized approach, it could happen. In fact, the entire push for conjunctive use has come about through the need to appease a wider number of water users while sustaining the resource. The treatment of institutions as static and unable to change is a problem.

Despite the limitations found in the three-state study and the treatment of institutions as being unable to change and adapt, Common Waters, Diverging Streams does make a significant contribution and deserves a positive recommendation on two fronts. Conjunctive use is going to be an important part of western water management for some time to come, and this work serves as a fine resource for anyone who wishes to understand how conjunctive management works. In addition, the way the three states are handled individually provides a good look at how institutions play a part in shaping policies and at how these policies are implemented—making the work a solid resource for anyone wishing to explore the complexities of public policy and management through the lens of western water management.