The world’s rivers support a wide range of human activities, including providing drinking water, supporting agriculture and power generation, and providing recreation and cultural activities.  Most of us interact with rivers—or the services they provide—on a daily basis.

Over the coming decade, it is predicted to cost over $114 billion per year to achieve Sustainable Development Goal 6 (water and sanitation). Essential to the success of SDG6 is maintaining the health of river ecosystems, which in turn, requires careful management to provide and protect environmental flows.  With increasingly scarce water resources and growing demands for water, how do we ensure the ongoing sustainability of our rivers?

To tackle this complex problem, most countries now have policies to allocate water to the environment. Historically, the focus has been: how much water does the environment need? Finding the “right” allocation of water between consumptive and environmental water uses is a question of allocative efficiency. However, once water is allocated to the environment, question becomes: how can we get the best outcomes from this water? This is a question of productive (or operational) efficiency, which has been largely overlooked in the context of environmental water management.

Productive efficiency is widely discussed in the context of private agricultural water users, who are in the more mature stages of water use patterns and knowledge. But environmental water managers are at an earlier stage of water use knowledge and practice development, and arguably require a greater focus on identifying and advancing arrangements that maximise sustainable ecosystem outcomes from available water in cost-effective ways. A  review in WIREs Water introduces and explores the concept of Environmental Water Use Efficiency.

The ability to use environmental water efficiently and effectively will influence the determination of how much water is needed, and indeed the outcomes possible from that water. The lowest upfront cost and most politically viable mechanisms to recover water may not provide the most effective means to manage environmental water in the longer term.  Acknowledging and understanding the implications of the institutional and water allocation arrangements for ongoing costs and benefits can help inform the ongoing political narrative and future policy directions.

Kindly contributed by Avril Horne.