What the research says
In a 2011 study, 21 men drank four or six mugs of black tea with a splash of milk, or the same amount of boiled water, over 12-hour periods. Their blood and urine hydration measures were the same with tea as with water, and the researchers concluded that tea hydrates as well as water.
The Beverage Hydration Index study tested both hot and cold tea. Neither differed from still water in how much fluid people kept in their bodies.
Caffeine in tea
A cup of black tea has around 50 mg of caffeine and green tea around 30 mg, against roughly 90 mg in a cup of filter coffee. A diuretic effect only shows up at much larger single doses, so everyday tea drinking does not dehydrate you. Herbal teas such as chamomile, rooibos or mint are naturally caffeine-free.
Milk tea, Thai tea and boba
Sweet milk teas are still mostly water, so they count. The catch is sugar: a large Thai tea or bubble tea can carry as much sugar as a can of soda, and the tapioca pearls are a snack, not a drink.
Waterie counts Thai tea and Thai green milk tea at 90% and boba tea at 85%. Those lower values are Waterie's own conservative choice for heavier, sweeter drinks, not a measured result.
How Waterie counts it
These are the values the app uses for tea drinks. A 250 ml cup of tea adds about 240 ml to your daily goal.
| Drink | Hydration value | 250 ml counts as |
|---|---|---|
| Tea | 95% | 238 ml |
| Black Tea | 95% | 238 ml |
| Green Tea | 95% | 238 ml |
| Herbal Tea | 95% | 238 ml |
| Matcha | 95% | 238 ml |
| Iced Tea | 95% | 238 ml |
| Thai Lemon Tea | 95% | 238 ml |
| Thai Tea | 90% | 225 ml |
| Thai Green Milk Tea | 90% | 225 ml |
| Boba Tea | 85% | 213 ml |
More questions
Does green tea dehydrate you?
No. Green tea has even less caffeine than black tea, and at normal amounts it hydrates like water. Waterie counts it at 95%.
Does herbal tea count as water?
Yes. Most herbal teas have no caffeine at all, so they are essentially flavoured water. Waterie counts herbal tea at 95%, the same as other teas.
Is iced tea as hydrating as hot tea?
Yes. Temperature does not change how well a drink hydrates. Unsweetened iced tea counts the same as hot tea. Bottled iced teas are often sweetened, which adds sugar but does not stop them counting.
Sources
- Ruxton CHS, Hart VA. Black tea is not significantly different from water in the maintenance of normal hydration in human subjects: results from a randomised controlled trial. British Journal of Nutrition, 2011. Funded by the Tea Advisory Panel, supported by the UK Tea Council.
- Maughan RJ, Watson P, Cordery PA, 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. Funded by the European Hydration Institute.
- EFSA Panel on Dietetic Products, Nutrition and Allergies. Scientific Opinion on the safety of caffeine. EFSA Journal, 2015.
Last reviewed 4 October 2026
General information for healthy adults, not medical advice. If you are pregnant or have a condition that affects your fluid balance, follow your doctor's advice.