Yasuhiro Sonoda appeared nervous and his hands shook as he downed a glass during a televised news conference.
The water he drank was taken from puddles under two reactor buildings. It is decontaminated before being used for tasks such as watering plants.
Journalists have repeatedly queried the safety of the procedure.
Mr Sonoda, who serves as the cabinet office’s parliamentary spokesman, told the news conference: “Just drinking [decontaminated water] doesn’t mean safety has been confirmed. Presenting data to the public is the best way.”
It's Interesting 
He may regret that later