I have been drinking a gallon of water a day for 20 years; I read that it was good for you in high school and I never stopped. And I look a lot younger than I am. Everyone is shocked to learn my age. As a personal trainer I always put my clients on no less than 3L/day. At first they say they can't, then they try, and then they tell me how one day they suddenly got thirsty if they had less than that amount, and how much more energy they have. I have seen this over and over and over again. It makes a huge difference. A lot of times people think they are hungry, and it's just the dehydrated body crying out for water. Their mid-afternoon sleepies go away as well, and many of them have stopped coffee too.

The times I have not done this I notice I have morning breath, and my skin looks older. I don't have morning breath on my normal water days. My pee is clear to lightest yellow with no odor.

Every chemical reaction in the body uses water. We breathe it out with every exhalation. It's important. Without enough water, the body is making do and everything is functioning at a sub-par level. Everything including the brain and organs. Skin is just a symptom of what is going on inside.

By the way, I'm 5'0" and 98 lbs. It has nothing to do with size. Bigger people might need more than a gallon - my large male athletic friends often drink 1.5 gallons. It's individual. Some people might need more, others less, but you don't know what's enough until you try it.

And from what I have learned from some very knowledgeable, cutting-edge nutritionist friends, no other liquid will do. Tea, juice, etc, though they contain water have a net dehydrating effect. you can't substitute them. I don't have the data on this, these are authorities I trust so you will have to find your own support for this but this is what I have been assured by some very high-level experts. They are better than no liquids, but water is #1.

And yes, I pee all day long. Small bladder? I don't know. I don't care. it's worth it. One thing that does happen is the body gets used to holding more - it seems people pee a loooooot in the very beginning, less so once the adaptation occurs, but still more than the average, prematurely aging, bad-breath dehydrated 'normal' person.

Also, I don't know if it's true, but I heard that part of the reason spinal discs compress is also dehydration. Another reason why people get shorter when they age? This one I don't know if it's true or not but I'm curious about. I think there are probably thousands of unseen benefits that all add up to improved health.