What studies found
- Four cups of coffee (2014) — 50 male coffee drinkers drank four mugs of coffee a day (4 mg caffeine per kg) or the same volume of water, over three-day periods. Body water and blood and urine markers did not differ.
- Beverage hydration index (2016) — 72 men drank 1 L of each of 13 drinks and urine output was measured. Milk, skimmed milk, an oral rehydration solution and orange juice were retained better than water; coffee, tea, cola, lager and a sports drink were similar to water.
- Valtin’s 2002 review likewise concluded caffeinated drinks count toward daily fluid for most people.
Drink by drink
| Drink | In studies | Keep in mind |
|---|---|---|
| Coffee, tea | Normal amounts similar to water | Watch total caffeine and late-day cups. |
| Milk | Retained better than water | Has calories. |
| Juice, soda | Similar or better | High in sugar; water is the better default. |
| Beer | Lager similar to water in a 1 L test | Stronger drinks were not tested. Alcohol is not a hydration strategy. |
Choose a logging rule
By the research, you can count coffee in full. But if your goal is a plain-water habit, filling it with coffee may not be what you want. Pick one rule and stick to it:
- Count everything — closest to the science; good for checking you are not short.
- Discount some drinks — count coffee and alcohol at less than full value to nudge yourself toward water.
Logging by drink type
The Android app "Water Tracker" uses the second rule. Each drink type has a factor that converts what you drank into a "hydration" amount added to your goal. The factors are the app’s own conservative settings meant to keep water as the base, not measured values.
| Drink | App factor | If you drink 350 ml |
|---|---|---|
| Water, sports drink | 100% | 350 ml |
| Tea | 95% | 333 ml |
| Coffee, milk, other | 90% | 315 ml |
| Juice, soda | 85% | 298 ml |
| Alcohol | 40% | 140 ml |
Add with drink type
On the Today tab, tap "Add with drink type" to pick a drink, amount and time. The log shows the original amount (for example "+350 ml · Coffee") and the goal counts the hydration amount.
Check your drink breakdown
The Drink breakdown on the History tab shows how much of your intake is water. If coffee dominates, try pairing every coffee with a glass of water.
FAQ
Coffee makes me go to the bathroom more, though.
Going more often is not the same as losing body water. In the trial above, hydration markers on coffee days matched water days.
Can a quick add button be coffee?
Yes. In Settings > Edit quick-add buttons, each button gets its own amount and drink type. The default 350 ml button is already coffee.
Sources: Killer et al., PLoS One 2014 (coffee and hydration) · Maughan et al., Am J Clin Nutr 2016 (beverage hydration index) · Valtin, Am J Physiol 2002, "Drink at least eight glasses of water a day." Really?
Water Tracker: Drink Reminder
No sign-up, and your drink log stays on your phone. Free on Android.