And while we're on the subject, how about Constitution?
The Player's Handbook says you can hold your breath for a number of minutes equal to 1 + your Constitution modifier. Without training, most of us can manage about 90 seconds underwater before needing to take a breath...so most of us have a Constitution score of 10-13, which sounds about right.
Well. On 28 February 2016, Spain's Aleix Segura Vendrell achieved the world record for breath-holding, with a time of 24 minutes. That's a Constitution modifier of +23, which means his Constitution score is at least 56.