Urban water security (UWS) is and will remain a crucial issue over the next decades, especially as it is exacerbated by climate change effects and related hazards. Despite the growing number of studies focusing on more diverse dimensions, including social dimensions, of water security and urban dynamics, there is still an absence of comprehensive, interdisciplinary UWS measurement index that takes into account the complexity and multidimensional aspects of water security. This article discusses a new, transdisciplinary community-focused approach to analyzing and responding to water insecurity. It draws on findings from a large study carried out over 4 years with a focus on creating a new and comprehensive way of measuring water security, incorporating biophysical and social factors. The project collected data in Kolkata, India. Kolkata is an important megacity in a developing country, facing rising pressures on water-environmental provision due to rapid population growth and urbanization combined with governance and infrastructural issues. The project team worked collaboratively with affected communities to create a comprehensive framework for measuring and evaluating water security for cities. A water justice approach to water security we argue is particularly important in emerging countries, and one that can be effectively applied to environments where urban growth and resultant shrinking resources have created complicated and fragile systems. This approach adds to existing knowledge and research that focuses on collaborative interdisciplinary methods that aim to create solutions that can help create a sustainable water secure future “leaving no one behind.