Can I actually drink too much water?

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It is possible to drink too much water. Doctors call this water intoxication. Water intoxication may cause electrolytes, such as sodium and potassium, in your bloodstream to get low. Low electrolytes can cause symptoms such as confusion or weakness. Water intoxication is rare. It is much more common for someone to be dehydrated from not drinking enough water than for someone to have water intoxication. When water intoxication occurs, it is usually in a patient who suffers from a psychiatric problem. In some of these cases, patients are drinking several gallons of water every day. It is hard to say how much water is too much, as we are all different, but generally, a healthy person would have to drink very large amounts of water to experience water intoxication.
A rare condition called hyponatremia (also known as water intoxication) can occur when extreme amounts of water are consumed during strenuous activity (more than 4 hours). In this condition, water intake is well beyond the amount of sweat loss, and there is not enough sodium (salt) in the body. Generally, the body cannot remove the excess water quickly enough.

Acute hyponatremia (occurring in less than 48 hours) can be a serious, life-threatening condition. Common symptoms include confusion, decreased consciousness, hallucinations, irritability, convulsions, fatigue, nausea, vomiting, headache, and muscle cramping. This rare condition can be prevented if sodium or a sports drink containing sodium is consumed during and after strenuous activity.

(This answer provided for NATA by the Appalachian State University Athletic Training Education Program.)
Dr. Michael Roizen, MD
Internal Medicine
Water intoxication or sickness from drinking too much water occurs where you exceed your capacity to get rid of water. Your capacity to excrete water is normally about 1000 milliliters per hour (which is about 4 glasses), so if you drink more than this, you will dilute your body salts.

If the capacity to excrete water is impaired, then even lesser rates of consumption will result in low sodium concentration in your blood. Kidney failure is one reason for such an impaired capacity. The other, major reason for a failure to excrete a water load is the presence of a hormone vasopressin--the antidiuretic hormone. This last explains the frequency of low sodium concentration in the blood in marathon runners: marathon runners sweat and become volume depleted, vasopressin rises, thirst increases and due to the vasopressin, the water load cannot be adequately excreted and salt concentration falls.
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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.