What the study found
In the Beverage Hydration Index study, 72 men each drank a litre of still water and of three other drinks, on different days, and the researchers measured how much urine they passed over the next four hours. Full-fat milk, skimmed milk and an oral rehydration solution all left more fluid in the body than still water did. Coffee, tea, cola, sparkling water, a sports drink and a lager did not differ from water.
An earlier study from the same group found milk also works well after exercise. People who drank low-fat milk after sweating were still in positive fluid balance five hours later, while those who drank water or a sports drink were not.
Why milk scores higher
Milk has sodium and potassium, which help the body hold on to water, and protein and fat, which slow how quickly the stomach empties. The fluid is absorbed more gradually, so less of it is passed as urine in the following hours.
That does not mean a glass of milk contains more water than a glass of water. It means more of the fluid stays in your body for longer.
Should you drink milk instead of water?
Not as a swap. A 250 ml glass of whole milk has around 150 calories, and the hydration advantage only showed up in a short, controlled study. Milk is a good drink to include, especially after exercise, but water is still the easiest everyday choice.
Why Waterie counts milk at 100%, not more
Waterie caps every drink at 100% of its volume, so a 250 ml glass of milk never counts as more than 250 ml. Counting milk above water would mean the app credits you with fluid you did not drink. Plant milks and yogurt drinks were not in the study, and the app counts them at 100% too.
How Waterie counts it
These are the values the app uses for milk drinks. Every value is capped at 100%, so a 250 ml glass of milk counts as 250 ml.
| Drink | Hydration value | 250 ml counts as |
|---|---|---|
| Milk | 100% | 250 ml |
| Plant Milk | 100% | 250 ml |
| Soy Milk | 100% | 250 ml |
| Oat Milk | 100% | 250 ml |
| Almond Milk | 100% | 250 ml |
| Chocolate Milk | 100% | 250 ml |
| Yogurt Drink | 100% | 250 ml |
| Pink Milk | 95% | 238 ml |
More questions
Does plant milk hydrate like cow's milk?
Probably close, but it was not tested. Soy milk is closest to cow's milk in protein, while almond and oat drinks have much less protein and fat. All of them are mostly water, and Waterie counts them at 100%.
Is chocolate milk good for hydration after exercise?
It hydrates like milk and adds carbohydrate, which is why it is popular after training. It also adds sugar, so it makes the most sense after a long or hard session.
Does milk count toward my daily water goal?
Yes. Milk is about 90% water and counts fully toward your goal in Waterie.
Sources
- 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.
- Shirreffs SM, Watson P, Maughan RJ. Milk as an effective post-exercise rehydration drink. British Journal of Nutrition, 2007. Funded by the Milk Development Council.
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.