The U.S. Nuclear Regulatory Commission said Thursday that the level of tritium in the water is well below limits that would make it dangerous to drink.
The leak was reported Wednesday at the Oconee Nuclear Station near Seneca. The NRC says water was being transferred from one chemical treatment pond to another and began seeping from the ground.
Officials say the leak was greater than 100 gallons of water.
Duke Energy runs the plant. A watchdog group is calling on the company to figure out why the leak happened and prevent future spills. Duke officials say the reporting was voluntary and that no one is at risk from the release.