Dr. Hasumura practices medicine in Minami Aoyama, Tokyo published a book about sayu (hot water) in 2010 which is now followed by millions of Japanese. The hot water should not be boiling, but should be moderately hot: between 50 and 60 Celsius (between 122 F and 140 F). First boil the water (not in microwave) and let it boild for 10 minutes, the let it cool down to 50 to 60 celsius.
