I mean, this is a funny troll, but I hope nobody actually packs 16 liters of water for a one day hike. This is a recipe for hyponatremia, a rare yet serious condition of too low blood sodium levels from overhydration.

I don't think most adults should need more than 3 liters of water for a day long hike if they are already properly hydrated. The idea is to hydrate for 24 hours before you exercise. Then during the exercise, you take small sips occasionally. After an hour, you may need to begin replacing lost electrolytes. You also want to drink more often at high elevation and in the cold.

You can actually check how much water you'll need during exercise. Weigh yourself, exercise for an hour, and weigh again. The lost weight is the water you lost and need to replenish.

In any case, you should be peeing every 2 to 4 hours. If the water is clear, you're hydrated. If the water is dark yellow, you're really not hydrated.