Water security is a major challenge for science and society. We review the rapidly growing literature on water security from the perspective of risk science and management. Competing definitions and indicators of water security reflect unsettled conceptual and methodological issues. However, risk concepts have become prevalent in defining water security; measuring it quantitatively; tracking indicators of hazards, exposure, and vulnerability; and informing management options to reduce water-related risks. We examine water security indicators and indices to identify thresholds for water-related risks across multiple dimensions of water security and examine how these vary across different scales and socioeconomic contexts. Water security indicators reveal a disparity in hazards and vulnerability across geographic and political-economic conditions. Recognition of water security as a major societal challenge has been closely followed by a strong commitment to academic, government, development, and policy responses. Pathways to water security capture the sequence of investments in institutions and infrastructure to reduce water-related risks and manage trade-offs. Two well-studied water management case studies illustrate the pathways to water security and the need for more systematic comparative assessment.