Oil exploration poses an inherent risk to water resources and water quality, exemplified by oil spills resulting from broken pipelines, underwater blowouts and oil transport vessel accidents. In these instances, as vulnerable to spilled oil, water is usually the first casualty, resulting in oil contaminated water. In an effort to ensure the sustainability of freshwater resources resilience in Small Island Developing States, (SIDS), desalination is increasingly used to provide potable water. Thus, oceanic oil spills are of significant relevance to the provision of a guaranteed supply of potable water. Trinidad and Tobago, an oil-producing (SIDS), with considerable oil and gas activities on land and in shallow coastal waters; can become increasingly stressed from oil spills, possibly leading to halting seawater intakes in the desalination process. A real-life seawater surface oil spill in the Gulf of Paria, south-west coast of Trinidad, not far from the largest desalination plant in the Caribbean, is investigated using numerical mathematical modelling to model the spill’s movement underwater. The trajectory plots produced and analysed, indicated that depending on key parameters of the oil and the current ambient conditions, an oil plume can travel significantly long horizontal distances underwater before destabilising. Inferences suggested that oily underwater and existing ambient conditions can potentially affect the desalination equipment. Hence, oil spill modelling is necessary to determine oil trajectory and further inform the decision-making process in determining the best location for constructing desalination plants so as to minimise disruption to the island’s domestic freshwater supply in oil spill events.