A study in the Marshall Islands shows the underground lens on Majuro atoll has shrunk significantly because the local water company was forced to pump water for the drought-suffering population.
Reports by the Japan International Research Center for Agriculture Sciences show that the El Nino-caused drought in the late 1990s made the lens get smaller.
It is estimated to hold 1.9 million cubic meters, presenting a huge resource of fresh water for the estimated 30,000 residents of the capital.
The research has highlighted the need for reservoir management, fixing leaks in the distribution system, and looking at operations and maintenance costs of any equipment used to ensure it is sustainable in the long-term.
Japanese water researchers have also been designing a prototype desalination unit for home use that they hope will be able to produce up to 50 gallons of fresh water daily.