Humberside Police issued the warning on Sunday morning after the officer rescued the man from floods in East Yorkshire.
The force wrote on its Facebook page to say: "We're reminding everyone of the dangers of going into flood water this morning after a young man in drink was found in the water by a patrol officer.
"Fortunately for him he was found in time but entering flood water either on foot or in cars can be incredibly dangerous. Please stay safe #keepingyousafe".
Parts of East Yorkshire were among the worst-affected in Britain this weekend, which was the third in a row for severe weather.
Six flood warnings were in place as roads and homes in Snaith, East Cowick and Gowdall were hit by rising water levels.
Levels are expected to remain high for several days, East Riding of Yorkshire Council said.