Reservoir depletion in the Bredasdorp Basin has resulted in increasing decommissioning costs and ageing offshore infrastructure, yet depleted reservoirs may present opportunities for alternative subsurface resource utilisation. This study investigates offshore aquifers in the Central Bredasdorp Basin, South Africa, as a potential supplementary water resource. Groundwater currently supplies approximately 56% of South Africa’s population, either as a primary source or in combination with surface water, highlighting the need to diversify water resources under growing climatic and socio-economic pressures (Department of Water and Sanitation, 2022). Although offshore aquifer research remains limited due to restricted data access and the traditional separation between petroleum geology and hydrogeology, recent studies demonstrate that industry-acquired seismic and well log data can be repurposed to characterise offshore fresh groundwater systems (Post et al., 2013; Micallef et al., 2020). Globally, sub-seafloor groundwater reserves containing brackish to low-salinity water are increasingly recognised as viable alternatives to seawater desalination as extraction technologies advance (Michael et al., 2017). This study focuses on the 14A aquifer, where salinities below 30 ppt are classified as fresh. Aquifer boundaries were mapped over approximately 2,300 km2 using three-dimensional seismic data integrated with wireline logs from 22 wells to estimate porosity, permeability, water saturation, and salinity. The reservoir comprises interbedded sandstone–shale lithologies with gross sand thicknesses ranging from 4 to 125 m, porosities of 10–17%, and core-derived permeabilities of 3–639 mD, indicating favourable hydraulic properties. The aquifer is laterally continuous over ~35 km with an estimated volume of 18.72 km3. Volumetric estimates suggest that the 14A sandstones could supply the City of Cape Town’s water demand for approximately 2.4 years, highlighting the potential role of offshore paleowater systems in enhancing long-term water security in South Africa.