A man called the fire brigade after overrunning his bath.
Firefighters were called at about midnight on Monday to reports of flooding at a family home in Addiscombe, south west London.
They found a man in his 20s, who lived with his parents, had turned on the bath taps and forgotten about them.
Firefighter Jim Parrish said: "I think the son had just run a bath and forgotten about it. It was a bit silly really. They probably could have just mopped it up themselves."