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Short answer: Yes. Coffee counts toward your daily water intake. The National Academies, which set U.S. water intake recommendations, concluded that caffeinated drinks can contribute to your daily hydration as much as non-caffeinated ones. Caffeine is a mild diuretic, so it can make you pee a bit more, but in a study of regular coffee drinkers, four cups a day kept them as hydrated as the same amount of water. The diuretic effect is mostly an issue with large doses in people who rarely have caffeine. Plain water is still a good main drink, and coffee is not a reason to drink less of it.
"Coffee doesn't count, it dehydrates you" is advice many people have heard for years. Here is what the official intake recommendations and the hydration studies actually say about coffee and water, how much fluid you need each day, and the few situations where the diuretic effect of caffeine is worth keeping in mind.
What you'll learn
- Whether coffee counts toward your daily water intake
- What studies show about coffee and hydration compared with water
- When caffeine's diuretic effect matters, and when it doesn't
- How much water you need a day, and how coffee fits in
- Signs of dehydration and who should be more careful
Does coffee count toward your water intake?
Yes. U.S. water recommendations count "total water," meaning water from all drinks and food, not just plain water. About 80% of the water people take in comes from drinking water and other beverages, including caffeinated ones, and about 20% comes from food (National Academies). After reviewing the evidence on caffeine, the National Academies panel concluded that caffeinated beverages can contribute as much as non-caffeinated options to meeting daily hydration needs (National Academies).
That makes sense when you look at what is in the cup. Brewed coffee is more than 99% water: 100 grams of brewed coffee contains 99.39 grams of water and 40 mg of caffeine (USDA FoodData Central).
Is coffee hydrating or dehydrating?
For most people who drink it regularly, coffee is hydrating. Caffeine is a diuretic, meaning it can make you urinate more (MedlinePlus), but the extra fluid you lose is smaller than the fluid in the coffee itself. A review of the research found that caffeine raises urine output mainly when people take large doses, at least 250 to 300 mg at once, after going days or weeks without caffeine. Regular coffee and tea drinkers develop a strong tolerance to this effect, and the amounts in standard servings appear to have no diuretic action (Maughan & Griffin, 2003).
The National Academies reached a similar view: the diuretic effect of caffeine may be short-lived, and there is no convincing evidence that caffeine leads to an overall loss of body water (National Academies).
What the research shows
These are the main studies on coffee, caffeine and hydration. Most were done in healthy young adults, often men.
| Study | Who | What it found |
|---|---|---|
| Coffee vs water for 3 days (Killer et al., 2014) | 50 men who usually drank 3 to 6 cups a day | Four 200 mL (about 7-ounce) cups of coffee a day kept them as hydrated as the same amount of water, with no difference in total body water or 24-hour urine (2,409 vs 2,428 mL). One author worked for a beverage company. |
| 13 drinks compared with water (Maughan et al., 2016) | 72 men, 1 liter of each drink | Urine output over 4 hours after coffee was not different from water. Milk and an oral rehydration drink were held onto better than water. |
| Caffeine and urine output, meta-analysis (Zhang et al., 2015) | 16 studies, median dose 300 mg | Caffeine increased urine by about 109 mL (about 16%) on average. The effect disappeared during exercise and was stronger in women than in men. |
| 11 days of controlled caffeine (Armstrong et al., 2005) | 59 healthy young men | Up to about 6 mg of caffeine per kilogram of body weight a day caused no signs of dehydration in blood or urine markers. |
| Review of caffeine and fluid balance (Maughan & Griffin, 2003) | Studies from 1966 to 2002 | Large single doses can briefly raise urine output in people not used to caffeine; regular drinkers develop strong tolerance. |
Does coffee hydrate you as much as water?
In the most direct comparison, yes. Regular coffee drinkers who had four cups of coffee a day for three days stayed just as hydrated as when they drank the same amount of water (Killer et al., 2014). In another trial, a liter of coffee led to no more urine over 4 hours than a liter of water (Maughan et al., 2016).
Two caveats: these studies were small and mostly in men, and in a meta-analysis women were more sensitive to caffeine's diuretic effect than men (Zhang et al., 2015). And while coffee counts, water has no caffeine, so it is the drink you can have as much of as you want. If you add milk to your coffee, that is fine too: in the drink comparison trial, milk was held onto better than water (Maughan et al., 2016).
How much water do you need a day, and how much can coffee cover?
The National Academies did not set a number of glasses of water. Instead, they found that women who appear to be well hydrated take in about 91 ounces (2.7 liters) of total water a day, and men about 125 ounces (3.7 liters), from all drinks and food combined. People who are very active or live in hot climates may need more. For most healthy people, letting thirst guide them is enough (National Academies).
| Women | Men | |
|---|---|---|
| Total water a day, from drinks and food | About 91 oz (2.7 L) | About 125 oz (3.7 L) |
| From drinks (about 80%), by our calculation | About 73 oz | About 100 oz |
| Two 8-oz cups of coffee | 16 oz, about a fifth of that | 16 oz, about a sixth of that |
So a couple of cups of coffee is a real, if modest, part of your daily fluids. The limit on how much coffee you drink is caffeine, not hydration. For most adults, the FDA cites up to 400 mg of caffeine a day, about two to three 12-ounce cups of coffee, as an amount not generally associated with negative effects (FDA). Too much caffeine can cause problems including restlessness, insomnia, a fast heart rate and dehydration (MedlinePlus). See how much caffeine is in your coffee and how much caffeine is too much.
When coffee's diuretic effect matters more
- You rarely drink caffeine. A large dose, around 250 to 300 mg or more at once, is more likely to make you pee more if you are not used to it (Maughan & Griffin, 2003).
- You have a lot at once. Big doses from strong cold brew, several espresso shots or energy drinks push you toward the amounts where the effect shows up.
- You are at rest. In the meta-analysis, the effect was stronger at rest than during exercise, where it disappeared, and stronger in women than in men (Zhang et al., 2015).
- Your coffee comes with alcohol. Alcohol is a different story. See does alcohol dehydrate you.
If caffeine is the concern, decaf keeps most of the fluid with very little caffeine. See does decaf coffee have caffeine.
Signs of dehydration, and who should be more careful
In adults, signs of dehydration include feeling very thirsty, a dry mouth, urinating and sweating less than usual, dark-colored urine, dry skin, feeling tired and dizziness (MedlinePlus). Older adults are more likely to become dehydrated because some people lose their sense of thirst as they age, and people who exercise or work outdoors in hot weather lose more fluid (MedlinePlus).
If you are an older adult, exercising hard in the heat or sick with vomiting or diarrhea, do not count on coffee as your main fluid; drink water as well. If your doctor has told you to limit fluids, or you are pregnant, have a heart condition or take medication, ask your doctor how much coffee and fluid are right for you.
Simple ways to fit coffee into your hydration
- Count it. Your coffee is part of your daily fluids; you do not need to "make up" for it with extra water.
- Keep water as your main drink. It has no caffeine, so there is no upper limit to worry about for normal drinking.
- Watch caffeine, not just cups. Stay within about 400 mg a day if you are a healthy adult (FDA).
- Let thirst guide you on ordinary days, and drink more when it is hot or you are active (National Academies).
- For a lighter afternoon cup, try decaf, tea or a mushroom coffee blend, which usually has less caffeine than regular coffee. See how much caffeine is in mushroom coffee.
Common myths (quick reality check)
Myth: Coffee doesn't count toward your water intake. Reality: The National Academies count all drinks, and concluded that caffeinated beverages can contribute as much as non-caffeinated ones.
Myth: Every cup of coffee needs a glass of water to make up for it. Reality: In regular coffee drinkers, four cups a day kept people as hydrated as the same amount of water.
Myth: Coffee makes you lose more fluid than it gives you. Reality: Brewed coffee is more than 99% water, and the extra urine from caffeine averaged about 109 mL in a meta-analysis, far less than a cup.
Frequently asked questions (FAQ)
Does coffee count as water intake?
Yes. U.S. water recommendations count water from all drinks and food, and the National Academies concluded that caffeinated drinks can contribute as much as non-caffeinated ones.
Is coffee dehydrating?
Not for most regular drinkers. Caffeine is a mild diuretic, but in a study of habitual coffee drinkers, four cups a day kept them as hydrated as water.
Does coffee hydrate you as much as water?
In direct comparisons, moderate coffee hydrated about as well as water. Water is still the best main drink because it has no caffeine.
How much coffee is too much for hydration?
Caffeine, not fluid, is the limit. For most healthy adults, the FDA cites up to 400 mg a day, about two to three 12-ounce cups.
Why does coffee make me pee so much?
Caffeine is a diuretic and coffee is mostly water. The effect is stronger with large doses, in people not used to caffeine, and in women at rest.
Does decaf coffee count as water intake?
Yes. Decaf is mostly water and has very little caffeine, so it counts toward your daily fluids.
How much water should I drink a day?
The National Academies found that well-hydrated women take in about 91 ounces and men about 125 ounces of total water a day from drinks and food, with about 80% from drinks.
Related guides
- Why does coffee make me tired?
- Does decaf coffee have caffeine?
- How much caffeine is in a cup of coffee?
- How much caffeine is too much?
- Does alcohol dehydrate you?
- Should you wait 90 minutes to drink coffee?
Disclaimer and when to seek help
This article is for general education and is not medical advice. These statements have not been evaluated by the Food and Drug Administration. Our products are not intended to diagnose, treat, cure, or prevent any disease. Talk to your health care provider if you have been told to limit fluids, are pregnant or breastfeeding, have a heart or kidney condition, or take medication. Get medical help for severe dehydration signs such as confusion, fainting or not urinating.
References
- National Academies of Sciences, Engineering, and Medicine. "Report Sets Dietary Intake Levels for Water, Salt, and Potassium To Maintain Health and Reduce Chronic Disease Risk" News release, February 11, 2004.
- Killer SC, Blannin AK, Jeukendrup AE. "No evidence of dehydration with moderate daily coffee intake: a counterbalanced cross-over study in a free-living population." PLoS One, 2014;9(1):e84154. doi:10.1371/journal.pone.0084154
- Maughan RJ, Griffin J. "Caffeine ingestion and fluid balance: a review." Journal of Human Nutrition and Dietetics, 2003;16(6):411-420. doi:10.1046/j.1365-277x.2003.00477.x
- Zhang Y, et al. "Caffeine and diuresis during rest and exercise: A meta-analysis." Journal of Science and Medicine in Sport, 2015;18(5):569-574. doi:10.1016/j.jsams.2014.07.017
- Armstrong LE, et al. "Fluid, electrolyte, and renal indices of hydration during 11 days of controlled caffeine consumption." International Journal of Sport Nutrition and Exercise Metabolism, 2005;15(3):252-265. doi:10.1123/ijsnem.15.3.252
- Maughan RJ, et al. "A randomized trial to assess the potential of different beverages to affect hydration status: development of a beverage hydration index." American Journal of Clinical Nutrition, 2016;103(3):717-723. doi:10.3945/ajcn.115.114769
- MedlinePlus (U.S. National Library of Medicine). "Caffeine". Last updated September 8, 2021.
- MedlinePlus (U.S. National Library of Medicine). "Dehydration". Last updated December 29, 2023.
- U.S. Department of Agriculture. FoodData Central, SR Legacy 171890: Beverages, coffee, brewed, prepared with tap water.
- U.S. Food and Drug Administration. "Spilling the Beans: How Much Caffeine Is Too Much?" Content current as of August 28, 2024.
