A private tri-state water group has settled in six years what remains a thorny issue for Georgia, Florida and Alabama after 20 years — the sharing of waters in the Apalachicola-Chattahoochee-Flint river basin. The ACF Stakeholders’ 56-member governing board unanimously agreed on a water management plan for the basin Wednesday, a decision made after two days of mostly closed meetings in Apalachicola, Fla. “This is a watershed moment — no pun intended,” said Joanna Cloud, executive director of the Gainesville-based Lake Lanier Association.