While a father in Michigan was "distracted for three to five minutes" talking to someone--or "playing football," I'm not quite clear--his one-year-and-a-day-old daughter got out of the house, onto the porch, and into a 5-gallon bucket of water that'd been left out for the dog. That was it.
Unfortunately, it's the first bullet point on the American Academy of Pediatrics' Home Water Hazard for Young Children page [go read it. I'll wait.]:
One-year-old drowns in bucket of water [Ann Arbor News, via Obscurestore]
"Children can drown in 5-gallon buckets"(pdf) [Acutally, since 1984 at least 275 have. cpsc.gov]
Unfortunately, I think this happens quite often. My mom knows someone whose granddaughter drowned in a bucket last year. Her mother was mopping the kitchen floor and left the room to answer the doorbell. The kid toddled over, fell in, and that was it.