Somewhere in every office there's a person who insists coffee "doesn't count" and a person who counts their fourth flat white as two glasses of water. They're both a bit wrong, and the truth is more interesting than either — interesting enough that we built Hydration Hero to weight drinks differently instead of treating every liquid as water.
Here's the drink-by-drink version.
Coffee and tea: yes, mostly
A cup of coffee is about 98% water, and that water does reach your bloodstream. The worry is caffeine, which is a mild diuretic — it makes your kidneys pass a little more water than they otherwise would. For decades that turned into "coffee dehydrates you", which overstates it badly.
The clearest test of this was a 2014 study that had regular coffee drinkers consume either four cups of coffee or the same volume of water a day, then measured hydration every way available. It found no meaningful difference. Two reasons: the diuretic effect of caffeine is small relative to the water in the cup, and people who drink coffee regularly develop a tolerance to it anyway.
So: coffee and tea hydrate. Just not quite as efficiently as water, and less so if you're not a habitual drinker, or if you're having a very strong one. Treating a coffee as roughly a glass of water is closer to the truth than treating it as zero — but it isn't a full glass, and it's why a tracker that gives it full credit is quietly flattering you.
Milk: better than water, oddly
This one surprises people. A 2016 study that ranked thirteen common drinks on how much fluid your body actually retained a few hours after drinking them found that full-cream and skim milk both beat plain water. So did oral rehydration solutions. The reason is that the protein, fat and natural electrolytes in milk slow how quickly it leaves the stomach and help the body hold on to the fluid, rather than passing it straight through.
That doesn't make milk a water replacement — it has kilojoules, and plenty of people don't tolerate it. But if you're wondering whether your morning latte "counts", the milk in it is doing more for you than the coffee is.
Juice and soft drink: they hydrate, at a cost
Juice and soft drinks are mostly water and hydrate roughly as well as water does. The catch is everything else in the glass. A 375 ml can of regular soft drink carries around ten teaspoons of sugar; a glass of orange juice isn't far behind. They'll keep you hydrated, but "hydrated" isn't the only thing your body is keeping score of. Sparkling water, for what it's worth, is just water with bubbles in it — it counts fully.
Sports drinks: for sport
Sports drinks exist for a specific job: replacing fluid, carbohydrate and salt during long or intense exercise — think an hour-plus of hard training, especially in the heat. In that setting they genuinely outperform water, because the sodium helps you retain fluid and the sugar keeps you going. Outside that setting, they're a sugary drink with a marketing budget. A desk day doesn't need electrolytes.
Alcohol: it works against you
Alcohol suppresses the hormone that tells your kidneys to conserve water, so you pass more fluid than you take in. How much depends on the strength of the drink. A light beer is dilute enough that the water in it roughly cancels the effect; wine and spirits are net dehydrating, and the effect scales with how much you drink. This is a large part of why a hangover feels the way it does.
The practical version: a beer isn't a glass of water, and a glass of wine is less than nothing. A glass of water between drinks — the advice everyone's heard and nobody follows — actually does work, which is why Hydration Hero nudges you toward one.
Food: the fifth of your intake nobody counts
Around a fifth of the water most people take in comes from food. Cucumber, watermelon, oranges, tomatoes, soup and yoghurt are all mostly water. This is the part of the "eight glasses" myth that got lost — the original recommendation explicitly included water from food. If you eat a lot of fruit and vegetables, you need fewer glasses than someone living on toast. (How much water you actually need is its own question, and we've written about it separately.)
Why your tracker should weight drinks
Put all that together and the problem with most water apps is obvious: they count volume, not hydration. Log a long black and a glass of water and they give you the same credit. Log a beer and they give you credit for that too. By the end of the day the progress bar says you're fine, and your body says otherwise.
Hydration Hero weights each drink by what it actually does for you. A coffee earns most of a glass. A beer earns very little. A glass of milk earns a bit extra. Your hero reacts accordingly — jittery after the third coffee, a bit wobbly after wine, cheering when you follow it with water — and the goal you're chasing reflects what your body is really getting, not what you poured.
It's a small difference in the maths and a big difference in whether the number on the screen means anything.
This article is general information, not medical advice. If you have a condition that affects fluid balance, or you've been told to limit or increase fluids, follow your doctor's guidance rather than an app's.