Does coffee count as water intake? What the hydration trial found
The short answer
Yes. In a 2016 trial, a litre of coffee, tea, cola, juice, lager or sparkling water left the body as urine no faster than a litre of still water, so in ordinary amounts they hydrate you just as well. Milk and oral rehydration solution were retained better than water. The old advice to discount coffee is not supported by that evidence.
Plenty of water trackers count a cup of coffee as only part of a glass. Some count it as a loss. The reasoning is that caffeine makes you pass more urine, so coffee “doesn’t count”. It is a reasonable guess, and when someone measured it, it did not hold up.
The trial
In 2016, Ronald Maughan and colleagues published a randomised trial in the American Journal of Clinical Nutrition. Seventy-two volunteers each drank a litre of a test drink, and the researchers measured how much urine they passed over the hours that followed. Less urine means more of the drink stayed in the body.
They compared still water with:
- coffee
- hot tea and iced tea
- cola and diet cola
- orange juice
- lager
- sparkling water
- a sports drink
- milk, full-fat and skimmed
- an oral rehydration solution
From those results they built a Beverage Hydration Index: how much of a drink is still in you after a few hours, compared with the same amount of water.
What it found
Coffee, both teas, both colas, orange juice, lager and sparkling water were not different from water. Milk and the oral rehydration solution were retained better. Their mix of protein, sugar and salts slows how fast the body passes the water on.
So for counting purposes, a 200 ml coffee is 200 ml of fluid. A 240 ml cup of tea is 240 ml.
What the trial did not show
A careful reading matters here, because “coffee is fine” is easy to stretch too far.
- One litre, once. Each person drank a single litre of the test drink. Very large doses of caffeine are a different question, and this trial does not answer it.
- A few hours, not a lifetime. It measured retention after one drink. It says nothing about sleep, sugar, or anything else a drink brings with it.
- Lager only. No wine or spirits were tested. Do not read it as permission to count whisky towards your water.
- Healthy volunteers. If a doctor has given you a fluid limit or told you to avoid caffeine, follow that.
Counting your coffee also does not mean coffee is the best way to drink your day’s water. It only means the cup you had is not working against you.
How to count your cups
Count every drink at its real volume. Water, tea, coffee, juice and soft drinks all go in one for one. If you want to be exact, milk earns a little extra.
Then compare the total with a target that already allows for food. The big published figures are for total water, and food supplies a fifth to a third of that. Our guide to how much water to drink a day works through EFSA, the US IOM and India’s ICMR-NIN figures, and what each leaves you to drink.
How Enough counts drinks
Enough, our water tracker for Android, counts your drinks the way this trial supports:
| Drink | Counted as |
|---|---|
| Water | its full volume |
| Coffee | its full volume |
| Tea | its full volume |
| Juice | its full volume |
| Soft drink | its full volume |
| Milk | one and a half times its volume |
Each line cites the trial on screen, so you can see why. The four buttons on the home screen can be set to what you actually drink, such as a 500 ml bottle, a 200 ml coffee or a 240 ml tea, so a cup is one tap.
Enough also shows a ceiling above your target, because more water is not always better. It needs no account, and your record stays on your phone.
- Water
- Health
