Many people now have scales which tell them their weight, body fat and body water percentage. This is great information - but it's also important to understand how water percentage works.
I have a full article on this site explaining how much percent of water you should have in your body. A link to that chart is below. Let's say you look at that chart and determine that your ideal body water percentage is 52-58%, and your scale says that you currently are only 40% water. Can you just drink a ton of water every day and "fill your body with water"?
The answer, of course, is NO :). Let's talk about why. First off, let's imagine that you are 5' tall, 300 pounds. If you think about this logically, that probably means that you have 200 pounds of fat on you. That is a BIG percentage of you that is fat. You would have to somehow super-bloat yourself with water in order to make even a slight change in your water percentage, compared with all of that fat. It would be both impossible and unhealthy for you to do that.
Also, keep in mind that the body does not store water like that! If your body thinks it's in a drought condition, i.e. because you don't drink enough water every day, it will in fact bloat a bit. It will cling to all water it gets as tightly as it can, because it thinks that water is vital for survival. It's only if you start to drink adequate water every day - the 8 glasses a day doctors recommend - that your body releases water in a normal cycle and you stop bloating.
This is really critical for health, because the water moving through your system and flushing out of you is how your body removes toxins. This ensures that vitamins get to all the corners of your body, that your metabolism burns smoothly, and that all the toxins flush out of your skin and organs. It is critical for good health that your body get that water coming in and out at a smooth rate.
So how do you get a healthy water percentage, if you are drinking a lot of water and it's all flushing out of you? The key here is that the water percentage is a *BALANCE* - it should be your natural water weight, balanced by your fat and muscle weights. If your water percentage is too low, it's not really an indication that you have too little water in you. It's an indication that you have far too much fat in you, that it is outweighing the water you should have.
Let's take an example that's easy to divide up numerically. Let's go with an aim of 55% water. Let's say you are 300 pounds and 5' tall. Let's say that 200 pounds of that is therefore fat. That is 66% of you that is fat. That only leaves 34% of you to be anything else - water, muscle, etc. You would have to gain 60 pounds of *pure water* to start approaching your proper water percentage. That simply can't happen!
Instead, as you lose fat, the percentage of you that is water will naturally rise. Let's say you drop down to 200 pounds. You now have 100 pounds of fat. This means you are 50% fat, and 50% "other stuff". Your water percentage is now much higher, perhaps approaching that 50%.
So the summary is that you can NOT drink a ton of water and expect it to bloat your body like some sort of space alien, to improve your water percentage. Yes, you have to drink adequate water every day to be healthy, and to lose weight. But the overall key in getting your body to have a good balance of components is to have your fat levels down to a proper level. Only then can your body have percentages that begin to work in harmony with each other.