This publication examines the critical issues surrounding water security (water shortage, water excess, inadequate water quality, the resilience of freshwater systems), providing a rationale for a risk-based approach and the management of trade-offs between water and other (sectoral and environmental) policies.    The report sets out a three-step process to "know", "target" and "manage" water risks: (1) appraising the risks, (2) judging the tolerability and acceptability of risks and weighing risk-risk trade-offs, and (3) calibrating appropriate responses.    The publication provides policy analysis and guidance on the use of market-based instruments and the complex links between water security and other policy objectives, such as food security, energy security, climate mitigation and biodiversity protection.