Yes — despite the long-standing myth that caffeine cancels out its own fluid content, coffee and tea both count meaningfully toward your daily water intake. Here's what the evidence actually shows.
Yes. For people who drink caffeine regularly, coffee and tea contribute to daily fluid intake in much the same way as water does. Modern research has largely overturned the older assumption that caffeine's mild diuretic effect cancels out the fluid in the drink itself.
Your daily fluid target already assumes drinks like tea, coffee and milk count — see your full personalised estimate.
Open the Water Intake Calculator →Caffeine is a mild diuretic — it can cause the kidneys to produce somewhat more urine for a period after consumption. This is real, measurable physiology, and it's the basis for the popular belief that coffee and tea leave you with a net fluid loss. But a diuretic effect on urine output is not the same thing as a net negative fluid balance across the whole drink.
The confusion largely comes from studies on caffeine in isolation (e.g. as a capsule) in people who don't normally consume it, rather than on coffee or tea as beverages consumed by habitual drinkers — two quite different situations.
A 2014 controlled cross-over study by Killer, Blannin and Jeukendrup, published in PLOS ONE, compared coffee to water in 50 male habitual coffee drinkers (3–6 cups a day) and found no significant differences across a wide range of blood and urine hydration markers between the two drinks. The diuretic effect of caffeine also appears to diminish with regular use, as the body adapts — a phenomenon called caffeine tolerance. This is one study in habituated male coffee drinkers rather than a universal finding for every population, but it is representative of the broader modern evidence base on this question.
In practice, this means: if you drink coffee or tea regularly, your body has adjusted, and the fluid in the drink is doing meaningful hydrating work, similar to water. The old advice to add an extra glass of water for every cup of coffee is not well supported by current evidence for regular drinkers.
| Drink | Approx. water content | Counts toward fluid intake? |
|---|---|---|
| Black coffee (240 mL cup) | ~98–99% | Yes |
| Black or green tea (240 mL cup) | ~99% | Yes |
| Milk | ~87% | Yes |
| Herbal/decaf tea | ~99% | Yes (and no caffeine consideration at all) |
| Diluted low-sugar squash/cordial | ~90%+ | Yes, in moderation |
| Alcoholic drinks | Varies | No — alcohol is a genuine diuretic and a net fluid loss at typical serving strengths |
It's worth distinguishing caffeine from alcohol here: alcohol has a much stronger, well-established diuretic effect that does produce a net fluid loss, which is a materially different situation from moderate coffee or tea.
Does coffee count towards water intake?
Yes. Research shows that for regular, moderate coffee drinkers, coffee contributes to overall fluid intake similarly to water — the old idea that it causes a net fluid deficit has not held up in controlled studies.
Does tea count as water intake?
Yes. Tea is over 99% water and, like coffee, contributes positively to daily fluid intake, including caffeinated varieties such as black, green and oolong tea.
Does coffee dehydrate you?
Not meaningfully for regular drinkers. Caffeine has a mild diuretic effect that can cause a small, temporary increase in urine output, but this does not outweigh the fluid volume of the drink itself in people who consume caffeine regularly. It may cause a brief diuretic effect in people who rarely consume caffeine.
Coffee and tea are both over 98% water and, for regular drinkers, contribute to daily fluid intake much like water does — the "cup of water for every cup of coffee" advice isn't well supported by current evidence. Alcohol is a different story and does cause a genuine net fluid loss. When estimating your daily water intake, it's reasonable to count your usual coffee and tea toward your fluid total.