The fortified Kinmen island group only two kilometres from the mainland was a flashpoint during the Cold War and was heavily shelled by Chinese forces in the late 1950s.
"Regarding the proposal for water imports from the mainland, the two sides have reached a consensus in the meeting," said a brief statement after a meeting in Kinmen between officials from the Taiwan county government and China's coastal Fujian province.
Details of the agreement, which needs final approval from higher authorities on both sides, were not released.
Currently the water company, via desalination, underground supplies and a tiny dam, can supply up to 19,000 tonnes of water daily -- 15,000 tonnes short of demand -- for some 100,000 civilians and troops stationed there.
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The officials will hold another meeting in Fujian's Quanzhou city next month to work out details such as the contract, pricing and construction costs, Wang said.
The Chinese army fired more than 470,000 shells on Kinmen, then known as Quemoy, and several other islets in a 44-day artillery bombardment beginning on August 23, 1958. They killed 618 servicemen and civilians and injured more than 2,600.
Tensions across the Taiwan Strait have eased since Taiwan's China-friendly President Ma Ying-jeou came to power in 2008, pledging to boost trade links and allow more mainland tourists. He was re-elected in 2012.
With the easing of tensions, Chinese tourists make hundreds of thousands of visits to Kinmen each year, accentuating the acute water shortage.
Taiwan and the mainland split in 1949 at the end of a civil war.