Can You Drink Too Much Water? What Hyponatremia Is

Yes, you can drink too much water, but in healthy people it’s rare. It usually takes a large amount in a short time, or a condition, medication or long endurance event that stops the body from getting rid of the extra.

The National Academies, which set US water guidelines, put it plainly: some athletes and some people with certain psychiatric conditions occasionally drink amounts of water that can be life-threatening, but “such occurrences are highly unusual,” and the panel did not set an upper limit for water. Here’s what actually happens when it goes wrong, who’s at risk, and what to watch for.

What happens when you drink too much water?

The problem is sodium, not water itself. When you take in more water than your kidneys can clear, the extra dilutes the sodium in your blood. That’s called hyponatremia, or low blood sodium. When it’s caused by drinking too much, it’s often called water intoxication.

MedlinePlus, the National Library of Medicine’s health site, explains why that matters: when sodium drops, water moves into cells and makes them swell, and swelling of brain cells is what makes severe cases dangerous. “When your body’s sodium level drops too much, it can be a life-threatening emergency.”

Hyponatremia isn’t only caused by drinking. MedlinePlus lists other causes too, including diuretic medicines (water pills), heart failure, kidney disease, cirrhosis, and heavy vomiting, diarrhea or sweating. So low sodium is a medical finding with many roots; overdrinking is one of them.

Who is at risk of water intoxication?

Most people who drink when they’re thirsty never come close. Cleveland Clinic lists the groups who are more at risk:

• Endurance athletes doing long runs, hikes, rides or other exercise with heavy sweating over many hours.
• People working in extreme heat, outdoors in hot weather or in hot buildings.
• People taking some antidepressants or antipsychotics, which can cause extreme thirst, and people taking NSAIDs (common pain relievers), which can make the kidneys hold on to water.
• People with chronic kidney disease, liver disease, congestive heart failure or SIADH, a condition in which the body makes too much of the hormone that tells the kidneys to keep water.
• People with psychogenic polydipsia, a compulsion to drink large amounts of water, and people who use MDMA.
• Babies under one year old, because of their small body size.

Is it a risk for runners and athletes?

It’s the best-studied group. The National Athletic Trainers’ Association’s position statement on fluid replacement says exercise-associated hyponatremia is caused by drinking too much low-sodium fluid, including sports drinks, often combined with the kidneys clearing less water during exercise. It’s “uncommon in team-sport athletes,” but has been found in 10% to 20% of distance athletes tested after events, more often in women than in men and after activity lasting more than 4 hours.

The key warning sign is gaining weight during exercise. If you weigh more after a long run than before it, you drank more than you sweated out. The statement’s advice is to replace only what you lose in sweat and not to gain fluid weight. If you don’t know your sweat rate, it says drinking to thirst “most likely represents a safe strategy to prevent overdrinking.” For more on fluids around exercise, see our workout hydration guide and electrolytes vs. water.

What are the signs of drinking too much water?

Cleveland Clinic groups the symptoms by severity:

• Early or mild: nausea, vomiting, a bloated stomach, headache, drowsiness, muscle weakness, pain or cramps, and swelling in the hands, feet and belly.
• Changes in thinking: confusion, irritability and dizziness.
• Severe, if untreated: seizures, delirium, coma and death.

Many early signs, like nausea, dizziness and headache, overlap with being under-hydrated. The athletic trainers’ statement notes that only a blood sodium test can tell the two apart, which is one reason to get checked rather than guess (and not to treat these symptoms by drinking even more).

Urine color is a rough clue. Cleveland Clinic says pale yellow is the goal, and “you may be drinking too much water if your pee is colorless or clear.”

How much water is too much?

There’s no single number for everyone, because it depends on your body, your health and how fast you drink. What the sources do say:

• Speed matters more than the daily total. Cleveland Clinic says the kidneys remove about 32 to 64 fl oz (1 to 2 liters) of excess water a day, and that in some people symptoms can develop after drinking about a gallon (3 to 4 liters) of water over an hour or two. Its guidance is that more than 32 fl oz (about a liter) of water per hour “is probably too much.”
• Babies are different. Cleveland Clinic advises that a baby who seems to need water should have no more than 3 fl oz.
• There’s no official daily ceiling for healthy adults. The National Academies chose not to set an upper limit, and note that very active people in hot weather often need 6 liters (about 200 fl oz) or more of total water a day.

For a sense of normal: the National Academies’ Adequate Intake for women is about 91 fl oz of total water a day from food and drinks, about 74 fl oz (9 cups) of it from drinks. Those are typical intakes for healthy people, not targets you have to force. You can see the full set of figures on our hydration statistics and women’s hydration statistics pages, or get a personal starting point from the water intake calculator.

Why most people don’t need to worry

The same body system that makes you thirsty also clears extra water. The National Academies concluded that “the vast majority of healthy people adequately meet their daily hydration needs by letting thirst be their guide.” Spreading your drinks across the day, the way most people naturally do, keeps you well inside what your kidneys can handle.

Where people get into trouble is forcing water: chugging large amounts in a short window for a challenge or a “flush,” or pushing fluids far past thirst during a long event. Rigid rules can encourage that. “Drink half your body weight in ounces” and “8 glasses a day” aren’t evidence-based rules, and our research on hydration myths found both still repeated as fact on Google’s first page.

When should you see a doctor?

Cleveland Clinic advises seeing a healthcare provider as soon as you or someone else shows signs of water intoxication; faster treatment lowers the risk of severe complications. If you feel nauseous, bloated or headachy, especially with colorless urine, stop drinking water. MedlinePlus says to call your provider right away if you have symptoms of hyponatremia.

Get emergency care (call 911) for confusion, a seizure, severe drowsiness or fainting, especially during or after a long endurance event or after drinking a large amount quickly.

And if you have kidney disease, heart failure or liver disease, or take medicines that affect fluid balance, talk to your provider before drinking large amounts. Your safe range may be different from the general guidelines.

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