What Is the Beverage Hydration Index (BHI)?

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Most trackers treat every drink the same: water counts, everything else is ignored or scored zero. The Beverage Hydration Index says that's wrong. It's a 2016 lab score, built by exercise scientist Ron Maughan and colleagues, that ranks how much fluid a drink keeps in your body over the next few hours, benchmarked against still water at 1.0. A few drinks beat that benchmark, and none of the thirteen tested drop to zero.

What BHI actually measures

BHI is not about how much liquid goes in. It's about how much stays, and for how long.

After you drink something, your kidneys start clearing the excess. A drink that empties fast and gets excreted quickly gives you a short hydration bump. One that lingers, because it carries protein, fat, sugar or electrolytes that slow gastric emptying and fluid loss, keeps you hydrated for longer. BHI turns that difference into a single number.

Water is the reference point, fixed at 1.00. A drink scoring 1.50 retained 50% more fluid than water did, measured the same way in the same people. A score below 1.00 would mean faster loss than water, but none of the other eight drinks tested (cola, diet cola, both teas, coffee, lager, sparkling water and a sports drink) differed from water by a statistically meaningful amount.

How Maughan measured it

The 2016 trial split the work across three UK exercise-science labs (Loughborough, Bangor and Stirling) and 72 healthy, fasted men. Each man drank 1 liter of still water, plus 1 liter of three more drinks out of a lineup of thirteen, over 30 minutes each time. Researchers then collected urine for the next 4 hours after every drink, so each non-water result could be compared against that same person's own water baseline, not someone else's.

Thirteen drinks went through the protocol in total: skimmed milk, full-fat milk, an oral rehydration solution (ORS), orange juice, cola, diet cola, hot tea, iced tea, coffee, lager, sparkling water, a sports drink and still water itself. Whatever came back out in urine over those four hours set the score. Keep less of it, score higher.

The leaderboard

Four drinks scored significantly above water at the 2-hour mark. Everything else in the panel, coffee and tea included, scored no differently than water at all.

That orange juice number carries an asterisk for a reason the headlines usually skip. Maughan's team also recalculated BHI after correcting for the water each drink already contains, since milk and juice aren't pure water to start with. Corrected, milk and ORS kept their lead. Orange juice's edge nearly disappeared, down to about 1.24, no longer significantly different from water (P=0.11).

Once corrected for the water each drink already contains, only milk and oral rehydration solution reliably beat plain water. Orange juice's edge is not statistically significant.

How to count your drinks with BHI

A tracker that scores milk the same as water is undercounting you. One that scores coffee or tea as zero is undercounting you the other way, since neither behaved differently from water in the study above.

So how should a drink actually count, day to day? Our honest answer: credit it close to what the research shows, not a flat zero and not a flat match to water. That's what we built Brim to do. Instead of tracking water alone, Brim credits every non-water drink by a version of this index (Premium): milk, tea, juice, soda and alcohol, each at a set percentage of a glass of water. The BHI Hydration Index Lookup lists every value we use, and you don't need Premium to see them; the percentages show for every user, free or not.

Our numbers aren't a straight copy of the lab. We cap coffee lower than the study would justify (more in our coffee breakdown), and credit milk at 130%, not the roughly 150% Maughan's panel measured. Cautious beats clever on a number as debated as orange juice's.

The honest limits

The 2016 trial is the field's best single dataset, but it is one dataset: 72 fasted men in the UK, one 4-hour window, one liter of one drink at a time. It says nothing specific about women, about smaller or larger volumes, or about how BHI shifts with heat, exercise or illness.

It also tested only thirteen drinks. Most of what people actually drink worldwide, from a regional soda to a herbal infusion, was never in the panel. Applying its logic to an untested drink is a reasonable estimate, not a measurement.

Key takeaways