The article deals with the questions of the emergence, persistence and change of policy paradigms. It focuses on the role that policy networks play in this process and draws on the literature of problem definition to explain this role. The paper investigates water policy in Israel in the years 1948–1997. The paper distinguishes among two water policy paradigms that have prevailed: the earlier paradigm was one of expanding water resources and agricultural production, followed by a paradigm of priority of agricultural expansion over water conservation. The paper also distinguishes among periods of anticipatory and reactive water policy and highlights the role of policy networks in formulating public policies.