The availability of fresh groundwater in the coastal Netherlands is increasingly threatened by sea level rise, saltwater intrusion, and growing demands from industry, agriculture, and population expansion. One method used to bridge the gap in freshwater supply is reverse osmosis (RO) systems, which treat brackish or salinized groundwater. The challenge lies in the disposal of brine, the concentrate water produced during RO. For decades, one alternative has been the reinjection of the brine into deeper, highly salinized aquifers, based on the assumption that the area’s several clay aquitards and depth-of-injection prevent any potential environmental impacts. However, the validity of these assumptions remains unclear. This study examines the long-term feasibility and environmental implications of shallow brackish groundwater abstraction and subsequent brine reinjection in the coastal Netherlands through a modelling approach. We use as a case study the area of the Delfland water board, a coastal area in the west of the Netherlands that presents extensive groundwater salinization issues and freshwater competition between industry, horticulture and drinking water companies. Numerous abstraction-reinjection configurations are tested throughout the area using small, local-scale, fast running models in an HPC environment. These local models are based and feed from a spatially and temporally downscaled regional model of Delfland derived from LHM fresh-salt (the national variable density model of the Netherlands). We then evaluate the effects over the salt mass exfiltration, shallow and deep groundwater heads and saltwater interfaces. With this approach, we intend to find the technical and environmental limitations of these systems and their susceptibility to climate change over a large area.