Like January, February is a good time for visiting Japan as the weather is usually sunny and dry and sightseeing spots are not crowded. The downside of a visit in winter are the relatively short days (sunset is around 5:30pm in Tokyo) and the vegetation's barren state.
1 A healthy person drinking approximately 2 liters of water per day makes 800 to 2000 ml of urine per 24 hours (4).  If the urinary system is healthy, the bladder can hold up to 16 ounces (2 cups) of urine comfortably for 2 to 5 hours (5).
As you can see, water intoxication and death from drinking too much water depends on the speed with which you drink it. You can drink the 1.6 gallons of water slowly over 24 hours without getting any water intoxication symptoms. However, if you drink it within an hour, you can die from water intoxication.