An international team of scientists may have found "freshened groundwater" offshore in the south-east of Malta.
The discovery, off the coastline between Valletta and Marsascala, could mean a new source of potable water, researchers said.
Scientists from Malta, Germany, Spain and Italy were involved in the study, which is based on an oceanographic expedition carried out in 2018.
Seismic reflection profiles acquired during this expedition were used to generate a geological model of the seafloor offshore the Maltese islands, with electromagnetic surveying carried out to identify resistivity anomalies, or high values of electromagnetic resistivity beneath the seafloor.
The observations indicate that freshened groundwater occurs as an isolated body hosted in Globigerina Limestone located three kilometres from the coast.
According to the researchers, numerical modelling suggests that there may be a second offshore groundwater body within one kilometre of the Maltese coastline.
They say the bulk of the groundwater was deposited 20,000 years ago when sea-level was lower than today.
"There are a number of important implications associated with this discovery," the researchers said.
"Offshore freshened groundwater may constitute a new, unconventional source of potable water that should be considered in future national water management strategies for the Maltese Islands."
The occurrence of freshened groundwater offshore a dry, limestone coastline such as the Maltese one "bodes well for similar settings in the Mediterranean region that are suffering from water scarcity", they noted.
"On the other hand, the exploitation of the Maltese offshore groundwater system is likely unsustainable, because it is not being actively recharged, and pumping rates are likely to be low," they added.
The study, which is a product of the MARCAN project, was published in international journal Geophysical Research Letters.
The MARCAN project is a five year research project that investigates the role of offshore groundwater in the geomorphic evolution of continental margins and is supported by the European Research Council.