All of these must be dissolved in water in order to be excreted from the body. If there's not enough water to dissolve these compounds, the waste can sit longer in the body. Men and especially women who don't drink enough water are more prone to painful urinary tract infections, because the urine is more concentrated and sits in the bladder longer before being eliminated. If you don't drink very much, the urine you make just sits in the bladder like a cess pool, encouraging the growth of bacteria. In the long run, forcing the kidneys to work without the proper amount of water can make them less efficient and prone to failure.
Water is an important player in the joints, too.
The cartilage between joints holds a lot of water, which functions as a lubricant, helping joints to move smoothly without friction. If there's not enough water, the joints can abrade one another as they slide back and forth. This can lead to joint deterioration and pain. Nonactive people need 12 ounce of water per pound of body weight each day. A more active, athletic person needs 23 of an ounce of water per pound of body weight.