Intrastate wars involving non-state armed groups (NSAGs) are becoming an increasingly common form of violent conflict. How water is used conflict is therefore an important area of research. While previous research has traditionally viewed the use of water by NSAGs as a military tool, the Islamic State of Iraq and Syria (ISIS) instrumentalised water for a range of reasons which has not been examined in previous research. This paper addresses this gap by analysing the range of violent and non-violent means ISIS used to instrumentalise water for both state-building and military ends, linking this to the rebel governance cycle. Secondary literature analysis and thematic analysis are used to identify patterns in ISIS’ instrumentalisation of water within pre-existing literature. This is conducted in conjunction with two case studies: water governance and control of dams between 2014 and 2018. This paper finds that ISIS primarily instrumentalised water in three ways. Firstly, ISIS monopolised and institutionalised control over water services to build legitimacy as a state-like actor, symbolised by their control over dams. Secondly, ISIS used water to demarcate the territorial and demographic boundaries of their ‘alternative’ state, managing water supply to specific groups and controlling dams to flood or redirect water. Thirdly, as their territorial control became increasingly under threat, ISIS instrumentalised water through ‘scorched earth’ tactics, abandoning their governance of water entirely from 2016. These findings suggest that a new hybrid understanding of how NSAG’s interact with water (and other resources and built infrastructure) is needed to better analyse their dynamic and varying behaviour and priorities.