Hydration · lesson 6 of 9
Beverages compared
What every common drink actually does for hydration — caffeine, sugar, and alcohol included.
6 min read · reviewed October 2026
"Does coffee count?" is the most common hydration question — and the answer surprises people. Almost every drink hydrates you; what separates them is what else comes along: caffeine, sugar, or alcohol.
Hydration value isn't all-or-nothing. Researchers even rank drinks on how much fluid your body retains over the following hours — and milk and oral-rehydration-style drinks actually beat plain water on that measure, because the sodium and other nutrients slow how fast you pee it out.
Common drinks, ranked by what they bring
The baseline. Hydrates fully, zero calories, zero downside. The default for most of your daily intake.
Net hydrating in normal amounts. Caffeine is a mild diuretic, but the fluid in the cup more than offsets it — habitual drinkers also adapt. Watch added sugar/syrups, not the water.
Surprisingly more hydrating than water over the next few hours — its protein, fat, sodium, and potassium slow gastric emptying and urine output. Also a real source of protein and calcium.
Water + sodium + sugar (carbs). Genuinely useful for long/hot exercise; mostly unnecessary sugar if you're sitting at a desk. Right tool, wrong setting for everyday sipping.
Hydrate, but carry a large sugar load — a single can/glass can be 25–40 g sugar. Juice has some nutrients; soda is essentially sweetened water. Occasional, not a hydration strategy.
Net dehydrating. It suppresses ADH (the hormone that tells kidneys to retain water), so you lose more fluid than the drink provides — especially with spirits. Alternate with water.
Why caffeine's diuretic effect barely matters
Caffeine makes you pee a little more, but the water in your coffee or tea more than makes up for it — so the cup is still a net plus for hydration.
How it works →
Caffeine modestly increases urine output by blocking adenosine receptors in the kidney and slightly raising renal blood flow. But the effect is small at typical doses and the volume of fluid consumed alongside it is large. Regular caffeine users also develop partial tolerance to the diuretic response, shrinking it further.
What the studies show →
Controlled trials comparing caffeinated and non-caffeinated beverages have repeatedly found no meaningful difference in 24-hour hydration status at moderate caffeine intakes (roughly up to ~3–4 mg/kg, i.e. a few cups of coffee). The old advice to subtract coffee from your water total is outdated. A genuinely large single dose on a non-habituated person can produce a transient diuretic effect — but for everyday moderate drinkers, coffee and tea count toward fluid intake.
Sugar in a typical can of soda or large glass of juice — roughly a day's worth of added sugar in one drink, with no satiety to offset it.
Source: Typical product nutrition labels (varies by brand and size)
Which of these is genuinely NET dehydrating?
- A cup of black coffee
- A glass of milk
- A beer or glass of wine
- Plain water
Show the answer →
C.A beer or glass of wine
Alcohol suppresses ADH (vasopressin), so you excrete more fluid than the drink supplies — the only common beverage that's reliably net dehydrating. Coffee is net hydrating in moderation, and milk is actually retained longer than plain water.