"You shouldn't pull your bathtub's plug during heavy rain," said Yutaka Takahashi, 88, who advocates integrated management of water-related disasters. The reason: Simultaneous draining can flood sewer systems.
"Good flood control means everyone working together like so," he said.
Takahashi is a professor emeritus at the University of Tokyo. Specialising in river engineering, he believes water damage cannot be prevented just by dikes and dams. Instead Takahashi stresses the importance of integrated flood management involving such measures as forest preservation in watershed areas.
He was chosen as a winner of the Japan Prize this year, which is presented to scientists and researchers who contribute to society.
In 1971, he published a book in which he wrote, "River improvement work gathers water downstream, which invites massive flooding."
The government gave him the cold shoulder but his theory led to present-day comprehensive flood control measures like the construction of reservoirs. Takahashi also stresses residents' participation in river administration - a view that was reflected in the river law revision in 1997.
His roots as a researcher stretch back to 1947, when Typhoon Kathleen left 1,900 people dead or missing. "I remember thinking that the first step of postwar reconstruction was to eliminate water-related disasters," Takahashi said.
He has continued to value the importance of visiting and directly observing 109 "Class A" rivers throughout the nation.
The flood researcher's attention has now turned to climate change, in light of the rising frequency of major floods. "When global warming causes sea levels to rise, I wonder if rivers can endure heavy typhoons and high tides. We must think 100 years ahead," stressed Takahashi. This is an issue he entrusts to generations.