At a time when the reliability of freshwater resources has become highly unpredictable, as a result of climate change and increased droughts frequency, the role of scientific evidence in forecasting the availability of seasonal water has become more critical. Australia is one of the driest inhabited continents. Its freshwater availability is highly variable, which poses unique problems for the management of the nation's water resources. Under Australia's federal system, water management challenges have been progressively dealt with through political institutions that rely on best available science to inform policy development. However, it could be argued that evidenced-based policy making is an impossible aim in a highly complex and uncertain political environment: that such a rational approach would be defeated by competing values and vested interests across stakeholders. This article demonstrates that, while science has a fundamental role to play in effective water resource management, the reality on the ground often diverges from the intended aim and does not always reflect efforts at reform. This article briefly reviews the Water Act 2007 (Cth) and comments on why policy makers need to manage rather than try to eliminate uncertainty to promote change.