Climate change and water are intricately linked. Water is the primary medium through which the impacts of climate change will be felt. Securing the water sector and enhancing water security is, therefore, imperative for any adaptive response to climate change. A precursor in improving water security is to first establish a mechanism to measure it. Only then can incremental and progressive actions be evaluated. This study has developed such a mechanism in the form of a water security assessment framework using an indictor-based methodology. The framework is developed for city-scale analysis because analyses at this scale is more useful in operationalizing water security enhancement. The framework has a three-layered structure comprising five dimensions (broad elements of water security), twelve indicators (areas of interest within the dimensions), and a set of potential variables that can be used to quantify the indicators. The framework has been developed to foster practical interventions for water security enhancement and not as a comparative tool for benchmarking. Hence, while the dimensions and indicators of the framework are fixed, the choice of variables is up to the city depending upon its context. This aspect of the framework, therefore, is meant to help cities introspect internally and move up the water security ladder. The framework culminates into a Water Security Index (WSI), measured on a scale from one to five. The scale is linear and hierarchical in its grade value. The framework was successfully used to assess the water security situation of Bangkok. The study also makes a case for scaling up this intervention for other major cities in Thailand, which can then help implement some of Thailand’s key climate change adaptation initiatives such as the Nationally Determined Contributions and the National Climate Change Master Plan.