Water is one of three focus areas (alongside land and energy) for the forthcoming European Report on Development (ERD) 2011-2012 on natural resources management for inclusive and sustainable growth. Absolute availability is the key constraint in some contexts, where water is being exploited beyond its renewal capacity, often at the expense of ecosystems. At its most extreme, such apparent cases of ‘physical scarcity’ provoke alarming warnings of ‘water wars’ between competing users.  But conceptualising and measuring water scarcity is not straightforward.