Mystery

I keep waiting for someone to come up with an answer.
This reminds me of that story....
Mary and John were found dead on the couch. There were no bullet holes; no sign of them drinking or eating anything, no knives, no indication of how they died. The only thing out of place was a pool of water on the floor and a fishbowl lying next to it.
How did they die?

It's been a long time since I thought of that one so I may not have done it justice.s