Aging bodies need at least six glasses of water every day. Because a young adult's body is 60% water, but this amount decreases with age. The result is the skin dries out, and the kidneys don't flush waste as well.
Drinking more water means the skin has less chance of becoming dry. And the water dilutes the salts and minerals that pass through the kidneys helping the prevent the formation of kidneys stones.
So, have a glass of water before going to bed. Take another two glasses during breaktime. Substitute water for that second and/or third cup of coffee.