How Much Water Is Too Much?
Who is at risk of overhydration, what the warning signs are, and when to see a doctor, with sources.
Short answer
There's no single number. The National Academies didn't set an upper limit for water, and Mayo Clinic calls drinking too much water rare in healthy adults. The danger is drinking more than your kidneys can clear, which dilutes the sodium in your blood. That's a problem most often reported in endurance athletes who overdrink, people on certain medicines, and people with heart, kidney or liver disease. For most healthy adults, drinking to thirst and sipping through the day is the approach the sources describe as safest. Some medicines and conditions can lower blood sodium even at normal intake, so ask a clinician if that applies to you.
Use the Daily Water Intake Calculator for a target based on your weight and activity.
What too much water actually does
The medical name is hyponatremia, which means the sodium level in your blood is too low. Mayo Clinic describes a healthy blood sodium level as 135 to 145 mmol/L and defines hyponatremia as below 135. Sodium helps control how much water sits in and around your cells. When too much water dilutes it, water moves into cells and they swell. In the brain that can be dangerous.
The kidneys are what normally protect you. They make more urine when you drink more, which is why you pee so much when you drink water. The trouble starts when water comes in faster than the kidneys can send it out. A 2015 international consensus statement on exercise-associated hyponatremia puts it as drinking above known maximal urine excretory rates. The statement doesn't give a per-hour amount, and neither do we.
- Step 1Water arrives faster than the kidneys can clear itNormally the kidneys keep up by making more urine. The 2015 consensus statement describes the problem as drinking above known maximal urine excretory rates.
- Step 2Blood sodium gets dilutedMayo Clinic puts a healthy level at 135 to 145 mmol/L and defines hyponatremia as below 135.
- Step 3Water moves into cells and they swellIn the brain that can be dangerous.
Too much water isn't the only cause of low sodium. The MedlinePlus page on low blood sodium lists burns, diarrhea, vomiting, heavy sweating, diuretics, heart failure, kidney disease, cirrhosis and a condition called SIADH, where the body doesn't clear water properly. That page doesn't name drinking too much water as a cause, so we aren't claiming it does. Mayo Clinic's page on hyponatremia does include it, along with those medical causes.
How common this is
Not very. When the National Academies set their water guidance in 2004, they said some strenuous athletes and some people with certain psychiatric disorders occasionally drink dangerous amounts, and that this is highly unusual. They also said most healthy people meet their needs by drinking when thirsty. The Academies didn't set an upper limit for water.
Mayo Clinic's page on daily water intake says the same thing in plainer terms: drinking too much water is rare in healthy adults, though some athletes may do it before long or intense workouts.
Who is at higher risk
Mayo Clinic lists these groups as being more likely to develop low blood sodium:
- Older adults
- People who take thiazide diuretics, some antidepressants, some pain medicines, or the drug ecstasy
- People with kidney disease, heart disease or SIADH
- Athletes who drink too much water during marathons, ultramarathons, triathlons and similar events
The consensus statement adds factors specific to exercise. These are drinking more than you lose through sweat and urine, gaining weight during exercise, exercising for more than about four hours, being less experienced or less trained for the event, a slow pace, a very high or very low body mass index, and easy access to fluids. It also notes that smaller people and slower participants are more likely to run into trouble when they drink more than they lose. The panel stated that excess fluid intake underlies all known fatal cases of exercise-associated hyponatremia.
One point from that statement is worth knowing if you reach for a sports drink to be safe. The panel notes that sports drinks have less sodium than your blood, so they don't prevent the problem when intake is excessive.
Warning signs
Mayo Clinic lists nausea and vomiting, headache, confusion, fatigue or drowsiness, restlessness or irritability, muscle weakness, cramps or spasms, seizures and coma. The consensus statement describes milder early signs during exercise as lightheadedness, dizziness, nausea, puffiness or weight gain, and describes more severe signs as vomiting, headache, confusion, seizures and coma.
Several of these overlap with dehydration, which is one reason people get this wrong. Headache, nausea and tiredness don't tell you which way you're off. The context does. If you have been drinking a lot, aren't very thirsty, and your urine is clear and plentiful, more water isn't the answer.
Where 64 oz and a gallon fit
People often ask whether a gallon is too much. We cover that in detail in Is a gallon of water a day too much? The short version is that none of the sources we read give a number of ounces or gallons that's safe or unsafe on its own. What matters is how fast you drink, how much you're sweating, and whether you have a condition or take a medicine that affects how your body handles water. The same is true of 64 oz, which we look at in Is 64 oz of water a day enough?
To give the numbers some shape, the table below compares a gallon with the drinks target from our own calculator for adults who don't exercise. A US gallon is 128 fl oz, or about 3.8 liters. This is a comparison with our estimate, not a medical limit. Exercise and heat raise the targets.
| Weight | Daily drinks target | A gallon is about |
|---|---|---|
| 120 lb | 59 oz | 2.2 times the target |
| 160 lb | 79 oz | 1.6 times the target |
| 200 lb | 100 oz | 1.3 times the target |
| 250 lb | 125 oz | About the same as the target |
If you want that number in bottles, the bottles in a gallon converter and the water bottles per day calculator do the math.
How to stay in a safe range
- Let thirst lead. The consensus panel calls drinking palatable fluids when you're thirsty the safest individualized strategy, and says the older advice to drink before you feel thirsty led to overdrinking.
- Check your urine. Mayo Clinic says you're probably getting enough if you aren't often thirsty and your urine is colorless or light yellow. Cleveland Clinic says urine doesn't need to be clear.
- Spread it out. Sip across the day instead of drinking a large amount at once, since the problem is intake outrunning the kidneys.
- In long events, don't drink more than you sweat. Gaining weight over a long run or ride is a flag that you took in more than you lost.
- Don't force it. A target is a guide for people who tend to forget to drink, not a quota to finish when you aren't thirsty.
When to see a doctor
Get emergency care for vomiting with confusion, seizures, or loss of consciousness. MedlinePlus notes that a sharp drop in sodium can be a life-threatening emergency.
Talk to a clinician if you're in an at-risk group and have nausea, headaches, cramping or weakness, or if you take a diuretic, an antidepressant or a pain medicine and are unsure how much to drink. Also ask if you have heart, kidney or liver disease. A clinician may set a fluid limit for you, and that limit replaces any general advice on this page.
Keep reading
- Sweat Rate CalculatorSee how much you lose per hour so you don't drink past it.
- Is a Gallon of Water a Day Too Much?Who a gallon fits and who it does not.
- Do You Need Electrolytes?When plain water is enough and when electrolytes may help.
- What Counts as Water IntakeCoffee, tea, sparkling water and food.
Frequently asked questions
Can you drink too much water in a day?
Yes, but it's uncommon in healthy adults. Mayo Clinic describes it as rare, and the National Academies call dangerous intake highly unusual and didn't set an upper limit. The risk comes from water outpacing your kidneys, which dilutes blood sodium.
Is a gallon of water a day too much?
None of the sources we read set a safe or unsafe amount in gallons. A gallon is 128 oz, which is above the drinks target our calculator gives for most adults who don't exercise. Our page on drinking a gallon a day goes through who it fits and who it may not.
What are the first signs of drinking too much water?
Early signs include nausea, headache, lightheadedness, puffiness or a feeling of swelling, and fatigue. Confusion, vomiting that doesn't stop, seizures or fainting are emergencies. Because these overlap with dehydration, think about how much you have been drinking and whether you are thirsty.
How fast is too fast to drink water?
We didn't find a sourced per-hour figure, so we aren't giving one. The 2015 consensus statement describes the problem as drinking above maximal urine excretion rates. Sipping through the day and not drinking past thirst keeps you well inside that.
Do sports drinks prevent water intoxication?
Not when you drink too much of them. The consensus panel points out that sports drinks contain less sodium than blood, so excessive intake can still lower blood sodium.
Do my medicines change how much water is safe?
They can. Mayo Clinic lists diuretics, some antidepressants and some pain medicines among the things that raise the risk of low blood sodium. If you take any of these, ask your clinician or pharmacist how much to drink.
Sources
- Mayo Clinic, "Hyponatremia: Symptoms and causes": https://www.mayoclinic.org/diseases-conditions/hyponatremia/symptoms-causes/syc-20373711
- MedlinePlus, "Hyponatremia": https://medlineplus.gov/ency/article/000394.htm
- National Academies of Sciences, Engineering, and Medicine, news release on dietary intake levels for water, salt, and potassium, Feb. 11, 2004: https://www.nationalacademies.org/news/report-sets-dietary-intake-levels-for-water-salt-and-potassium-to-maintain-health-and-reduce-chronic-disease-risk
- Mayo Clinic Staff, "Water: How much should you drink every day?": https://www.mayoclinic.org/healthy-lifestyle/nutrition-and-healthy-eating/in-depth/water/art-20044256
- Hew-Butler T, Rosner MH, Fowkes-Godek S, et al. Statement of the 3rd International Exercise-Associated Hyponatremia Consensus Development Conference, Carlsbad, California, 2015. British Journal of Sports Medicine, volume 49, issue 22, pages 1432 to 1446. Citation details via PubMed: https://pubmed.ncbi.nlm.nih.gov/26227507/ (DOI 10.1136/bjsports-2015-095004). Text read at https://bjsm.bmj.com/content/49/22/1432
- National Academies Press. Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate, 2005. Water chapter: https://www.nationalacademies.org/read/10925/chapter/6
- Cleveland Clinic Health Essentials, "Are There Any Health Benefits to Drinking a Gallon of Water a Day?": https://health.clevelandclinic.org/are-there-any-health-benefits-to-drinking-a-gallon-of-water-a-day
How this page was built. This guide was drafted with AI assistance for Daily Water Calculator from clinical references and one consensus statement. The definition, causes and symptoms of low blood sodium come from Mayo Clinic and MedlinePlus, the points about thirst and the lack of an upper limit come from the National Academies, and the exercise risk factors come from the 2015 exercise-associated hyponatremia consensus statement. The comparison table is computed with the same code as the calculator. Where a source gives no number, such as an hourly limit, this page says so and doesn't supply one. We recheck the linked pages when we update the calculator. Last reviewed: .
General information for healthy adults, not medical advice. If you are pregnant or breastfeeding, or you have kidney, heart or liver conditions or a fluid limit, ask a clinician first. Terms and medical disclaimer.