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).
Over-hydration and water intoxication happens when you drink more water than your kidneys can get rid of via urine. But the amount of water isn't the only factor. How long you take to drink the water also counts. You have a greater risk of developing water intoxication if you drink a lot of water in a short period of time. The risk is less if you drink the same amount over a much longer period of time. Symptoms of hyponatremia can occur from as little as 0.8-1 gallons (3-4 liters) of water in a short amount of time .