In numerous coastal regions the salt/fresh water interface is moving landward. However, it may also be located 10s of kilometres seaward on the ocean shelf, indicating the presence of offshore freshened groundwater resources. The genesis of these offshore freshened groundwater (OFG) resources most probably dates back to previous glacial periods when sea levels were substantially lower, facilitating the deposition of freshwater in the land and now marine sediments (Fig. 1). While some of these offshore brackish lenses are disconnected from present-day land systems, others continue to be replenished by land-based aquifers, generating SGD. OFG bodies depend on long-term processes that are driven from within the catchments that recharge the hydraulically transmissive sedimentary bodies along the global coastlines. There are certain prerequisites that are necessary to facilitate the formation and preservation of freshwater in (nowadays) offshore aquifers. These are (i) the hydrogeological composition of the feeding terrestrial catchments, (ii) permeable shelf sediments hosting the OFG and particularly important (iii) either a fine-grained sediment cover, acting as an impermeable layer and protecting freshwater from seawater infiltration or (iv) effective hydraulic gradients between groundwater tables on land, hydraulically connected to the OFG bodies and the sea level. Climatic factors in conjunction with the catchment topography, in particular slope and drainage patterns, control the volume and pressure of freshwater transported towards the coast, which allowed flushing of shelf sediments during sea level low stands and can now contribute to a continuous recharge of the onshore-connected OFG bodies. OFG research faces two main challenges: (1) there is very limited data on the extent of global OFG bodies and most of this data data is present as point source data rather than areal information. (2) the majority of past hydrogeological studies have not taken into account the onshore-offshore connectivity of aquifers. There are only a few places along the Earth’s approximately 350 000 km length of coast, where systematic studies of offshore freshened groundwater based on 2D marine geophysical data and amphibious hydrogeological models have been investigated [1, 2]. Expensive geophysical exploration techniques, in particular marine electromagnetics, are useful for the identification and characterisation (eg. volume, salinity gradients and coastal connectivity, [3])