Can you drink too much water?

2026-10-30

Yes. Drinking far more water than your kidneys can get rid of dilutes the sodium in your blood, a condition called hyponatremia. In its severe form it can cause confusion, seizures and even death. It is rare in everyday life: healthy kidneys can clear a lot of water over a day, and the risk comes from drinking very large amounts in a short time, mostly during long endurance events, water-drinking challenges or with certain medical conditions and drugs.

What happens when you overdo it

Your body keeps the sodium level in your blood within a tight range. When you drink, your kidneys adjust how much urine you make so that balance holds. Trouble starts when water comes in faster than the kidneys can send it out, or when hormones tell the kidneys to hold on to water even though you have plenty.

The extra water dilutes the blood. To even things out, water moves into cells, and they swell. Most tissues tolerate that, but the brain sits inside the skull with little room to expand. Swelling there causes the symptoms of water intoxication, and in severe cases it can be fatal. Doctors call blood sodium below 135 mmol/L hyponatremia.

How much is too much?

There is no single number that is safe for everyone, but a few reference points help.

Per hour. A healthy adult's kidneys can only excrete a limited amount of water per hour. Figures of roughly 0.8 to 1 liter per hour at rest are often quoted, but this is an estimate, not a precise limit, and it is lower for smaller people and during long exercise. For workers in hot conditions, the US National Institute for Occupational Safety and Health advises in its heat stress hydration fact sheet to drink about 1 cup (8 fl oz, about 240 ml) every 15 to 20 minutes, and not more than 48 fl oz (about 1.4 liters) per hour, even while sweating heavily.
Per day. For most adults, healthy daily intakes are in the range of 2 to 4 liters from drinks and food, more in heat or with hard exercise. See how much water you should drink a day. Several liters in a few hours, on top of normal drinks, is where cases tend to appear.

If you drink to thirst and spread your intake across the day, you are very unlikely to get anywhere near these levels.

Who is actually at risk

Endurance athletes

This is the best-documented group. A study of the 2002 Boston Marathon took blood from 488 runners at the finish line: 13% had hyponatremia, and 0.6% (3 runners) had critically low sodium. The strongest predictors were:

gaining weight during the race, which means drinking more than was sweated out
finishing in over 4 hours, compared with under 3.5 hours (slower runners have more time to drink and sweat less)
very low or very high body mass index

Type of drink did not matter: sports drinks did not protect runners who drank too much of them, because they contain far less sodium than blood. The international consensus statement on exercise-associated hyponatremia concluded that the main cause is drinking more than you lose, made worse by hormones released during long exercise that cause the kidneys to retain water. Its advice is to drink according to thirst rather than to a fixed schedule or "as much as possible". For race-day details, see hydration for runners.

Other situations

Mayo Clinic lists several other causes and risk factors for low sodium:

Water-drinking contests and "challenges" that involve drinking liters quickly
The drug MDMA (ecstasy), which increases thirst and makes the kidneys retain water
Some medicines, including thiazide diuretics, some antidepressants and pain medicines
Conditions such as heart failure, kidney disease, liver disease, and hormonal problems
Older age, because of medicines and health conditions that affect water balance
Certain psychiatric conditions that involve compulsive drinking

Babies are also vulnerable. Infants under about six months should not be given plain water unless a health professional advises it; formula or breast milk covers their needs.

Warning signs of hyponatremia

Early symptoms are vague and can look like dehydration, which is what makes them dangerous: the wrong response is to drink even more. Watch for:

nausea and vomiting
headache
confusion, irritability or restlessness
tiredness and low energy
muscle weakness, cramps or spasms
in severe cases, seizures and loss of consciousness

A useful clue during endurance events: if you feel unwell, your stomach sloshes, your hands and fingers are swollen and you have been drinking a lot, or you weigh more after exercise than before, overdrinking is more likely than dehydration.

Severe symptoms such as confusion, seizures or reduced consciousness are a medical emergency. Call your emergency number. Don't give more water, and mention that the person may have been drinking a lot, as treatment is very different from dehydration.

How to drink safely

For most people, staying safe is simple:

Drink to thirst and keep an eye on urine color. Pale straw is the goal; clear urine all day means you can drink a little less. See what your urine color says.
Spread your intake out instead of downing big amounts at once. A glass at a time adds up.
During long exercise, drink to thirst and don't aim to "stay ahead". Weighing yourself before and after a long session tells you a lot: you should not end up heavier.
Replace salt when you sweat for hours. In long, hot events, salty snacks or electrolyte products help, though they don't make overdrinking safe.
Skip water challenges. There is no benefit to drinking several liters fast.
Talk to your doctor if you have heart, kidney or liver disease, take diuretics or other medicines that affect sodium, or have been told to limit fluids. Your safe range may be very different.

Where tracking fits in

Logging your water is usually about drinking enough, but it also helps you avoid the opposite. Water Tracker suggests a daily goal from your weight and activity, kept between 1.5 and 4 liters, so you have a sensible target rather than a "more is better" mindset. Its reminders go quiet once you reach the goal, so you are not nudged to keep drinking for the sake of it.

Bottom line

You can drink too much water, but for healthy people going about a normal day it is very unlikely. The risk comes from drinking large volumes quickly: several liters in a few hours, more than about a liter an hour for long stretches, or drinking well beyond thirst during endurance events. Drink to thirst, spread it out, aim for pale urine, and never respond to confusion or vomiting after heavy drinking by giving even more water.

This article is general information, not medical advice. If you have a health condition, are pregnant or take medication, ask your doctor how much you should drink.