What does water do when built up in the body?

It can cause edema, whether it be peripherally, pulmonary, or cerebral. Peripheral edema when controlled may be completely harmless. Pulmonary edema can affect gas exchange, literally causing a person to drown in their own lungs. Cerebral edema is swelling in the brain, which can lead to permanent brain damage. Good news? Usually you can take a diuretic (water pill) and get rid of most excess water in the body in very little time.