Water security is one of the biggest challenges of the 21st century. Understanding context-specific challenges and opportunities around this issue is key to improving water systems globally. This paper explores the current state of urban water security in Ulaanbaatar, Mongolia’s capital city. Ulaanbaatar is home to more than 40% of the country’s population and 60% of its national GDP. The city is located in the Tuul River basin and relies almost entirely on groundwater aquifers of the Tuul River for its supply of clean drinking water. In recent years, socio-economic stressors resulting from rapid urbanisation and environmental pressures have intensified the levels of degradation of the Tuul River and intensified the risks of water insecurity for the population of Ulaanbaatar. First, this paper draws from an extensive literature review and document analysis to provide an overview of the current state of urban water security in Ulaanbaatar. Secondly, the discussion is substantiated with information from key informant interviews which aim to explain the ongoing challenges for water security in Ulaanbaatar and suggest paths for improvement. This study finds that the main challenges for water security in Ulaanbaatar are data unavailability, limited human and financial resources across public water sector agencies, exacerbating flood risk and ongoing water quality disparities between the central city area and peri-urban ger districts.