The human body is full of water -- it's 55 percent to 75 percent of what we are [source: ASA]. Water flushes toxins out of the body, allows our cells to absorb nutrients, and keeps our digestive processes moving smoothly.
But that water isn't a constant. The most basic bodily processes, like breathing and sweating, remove that water from our cells. So for our cells to function properly, we need to consume lots of water to replace what we lose.
The skin is no different from the rest of the body when it comes to needing hydration. Water helps to remove impurities from the skin that can lead to pimples, and it hydrates to keep the skin looking plump and smooth.
To keep the skin hydrated, you should drink at least half a gallon (2 liters) of water each day [source: Edgar].
Up next: Water doesn't do much good if your cells can't hold on to it.