Droughts are natural hazards, to which irrigators must adapt. Climate change is expected to increase both the frequency and severity of future droughts. A common adaptation is investment in water-efficient technology. However, increased efficiency can paradoxically result in rebound effects: higher resource demand among consumptive users, and lower flow benefits for environmental users. Under an assumption of increasing future drought conditions, we examine anticipated rebound effect impacts on environmental and private irrigator water availability/use outcomes from current water efficiency-centric policy in Australia’s Murray–Darling Basin. We determine that rebound effects for environmental and private irrigation interests are likely. Our results identify greater technological change and higher consumptive land and water demand in northern Basin annual production systems, as irrigators switch to perennial cropping systems under subsidization incentives. Policy incentives to encourage water use efficiency paradoxically reduce environmental flow volumes on average. We find that environmental policy objectives will only be achieved when water is not a binding production constraint, typically in wet states of nature.