Garner, who stars in Columbia Pictures' "Catch and Release," said the mishap occurred while she was primping for the movie's premiere.
"He gave me this beautiful diamond ring and I was playing with it and ... it fell off. And it fell under this ice maker in the house he (Affleck) hasn't even heard of this yet and ... it fell into the drain under this ice maker," the 34-year-old actress said on "Live With Regis and Kelly."
"And the plumber had to come and dismantle the thing from under the house. And he found it," she said, holding up her hand to flash the sparkler, reports AP.
"And Ben hasn't even heard that," said co-host Regis Philbin.
"I should have warned him," Garner replied.
Garner and Affleck, 34, were married in June 2005. Violet was born later that year.
"Catch and Release" opens Friday.