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Measured against water

Does Coke hydrate you? Soda and diet soda vs water

Hydrates — no different from water over 2 hours

Yes. Coke is about 89% water, and the 34 mg of caffeine in a 12 fl oz can is far below the 250-300 mg it takes to measurably raise urine output, so the fluid stays in about as well as water does. In the one trial that measured it, neither cola nor diet cola differed from still water over two hours. What a can adds is 39 g of sugar and 140 calories — the reason to keep it occasional, not a hydration problem.1,2,3,4

Count your can
Cola
1.231
Hydration index 2 h after drinking; water is 1.00. Not a significant difference.
Diet cola
1.081
Same measure. Also no different from water.
Caffeine in a can
34 mg2
A 12 fl oz can of Coke — about a seventh of the 250-300 mg where diuresis becomes measurable.
Sugar in that can
39 g4
With 140 calories. Roughly nine to ten teaspoons.

Last reviewed 34 sourcesWritten from the studies, not from other websites

The measurement

Is soda hydrating? Cola and diet cola against water

The beverage hydration index compares the urine you pass after a drink with the urine after the same volume of still water: above 1.00 means more of the drink stayed in you. In the 2016 trial that created it, 72 healthy men each drank still water and three of the twelve other drinks, a litre at a time on separate mornings. Cola came out at 1.23 and diet cola at 1.08, and neither differed significantly from water. That 1.23 is not "cola beats water": the measurement repeats with a coefficient of variation of 18%, and cola is only 89% water — corrected for that, it falls to 1.09. The drinks that did clear the bar were skimmed milk (1.58), an oral rehydration solution (1.54), full-fat milk (1.50) and orange juice (1.39).

This pageAbove waterNo differenceWater = 1.00
  • Skimmed milk1.58
  • Oral rehydration solution1.54
  • Full-fat milk1.50
  • Orange juice1.39
  • Cola1.23
  • Diet cola1.08
  • Cold black tea1.07
  • Hot black tea1.03
  • Sports drink1.02
  • Still waterreference1.00
  • Lager0.99
  • Sparkling water0.98
  • Coffee (hot, black)0.91

Significance as marked on the paper’s Figure 2: ** P<0.01, * P<0.05 vs waterWhiskers are 1 SD

BHI = urine after still water ÷ urine after the test drink, 2 h after drinking ended. 72 healthy, recreationally active men aged 18-35, rested, fasted overnight and euhydrated. 1 L of each drink over 30 min in four equal portions; urine collected hourly for 4 h after drinking ended. Each man drank still water plus 3 of the 12 other drinks on separate mornings. Cold drinks 4-6 C, hot tea and coffee 60 C.1Funding: Funded by a grant from the European Hydration Institute (EHI). Prof Maughan chairs the EHI Scientific Advisory Board (not the Institute itself); Dr Watson has also received EHI funding.
Show the data table
Two-hour beverage hydration index for every drink tested, with standard deviations and how each was reported
DrinkIndex2 hCorrectedwater contentSDvs watern
Skimmed milkTesco, 0.1% fat1.581.440.60Above water17
Oral rehydration solutionDioralyte, made up with Highland Spring water1.541.500.74Above water17
Full-fat milkTesco, 3.6% fat1.501.320.58Above water17
Orange juiceTesco Everyday Value1.391.240.64≈Above water16
ColaCoca-Cola1.231.090.54≈No detected difference17
Diet colaDiet Coke1.081.080.24≈No detected difference16
Cold black teaPG tips1.071.070.59≈No detected difference17
Hot black teaPG tips1.031.030.24≈No detected difference15
Sports drinkPowerade1.020.980.24≈No detected difference17
Still waterHighland Spring1.001.00—Reference drink72
LagerCarling0.990.940.31≈No detected difference17
Sparkling waterHighland Spring0.980.980.20≈No detected difference17
Coffee (hot, black)Nescafe Original instant0.910.900.31≈No detected difference17

≈ marks a standard deviation read from the paper’s figures rather than its text. “Corrected” adjusts each drink for its own water content, which is the fairer comparison and the one that moves orange juice below significance.

What this number is not

  • — About 17 drinkers per test drink against a pooled water arm, so small differences such as coffee vs water cannot be detected.
  • — Rested, already-hydrated young men drinking 1 L in 30 min; the result describes a 2-4 h window, not all-day hydration.
Bar chart of the hydration index 2 h after finishing 1 L in rested, already-hydrated young men: cola 1.23, cola corrected for water content 1.09, diet cola 1.08, still water 1.00. Cola and diet cola showed no detected difference from still water.
In the 2016 trial that created the beverage hydration index, rested, already-hydrated young men drank 1 L in 30 minutes. Cola scored 1.23, or 1.09 once corrected for its water content, and diet cola 1.08; neither differed significantly from still water two hours after drinking ended.1 Open full size

The catch

If soda hydrates, why pick water?

Hydration is the one thing soda is not being criticised for here. The catch is what rides along with the fluid, and one situation — hard work in the heat — where a small human trial points to water instead.

  • The sugar is the whole objection

    A 12 fl oz can of Coca-Cola is 39 g of sugar and 140 calories; the 20 fl oz bottle is 65 g and 240. A can of Sprite is 38 g. The CDC's line on sodas, fruit drinks, sports drinks and energy drinks is that they carry calories with little nutritional value — which is a statement about nutrition, not about fluid, and it is the reason this page ends where it does.4,5,6

  • Swapping one can for water is the whole play

    It is also a small one, and worth being honest about: swap a daily can of cola for the same volume of water and you keep the fluid — about 332 mL of it — while dropping 39 g of sugar and 140 calories. Water Goose logs both at full volume, so the chart line does not move. Only what came with the fluid does.4,7

  • Caffeine matters when you are stacking it

    A can of Coke is 34 mg and a Diet Coke 46 mg, so soda on its own rarely takes anyone near a limit. The drinks people line up next to it are another matter: 80 mg in a small Red Bull, 114 mg in a 12 fl oz can, 200 mg in a can of Celsius. EFSA puts single doses up to 200 mg, and habitual intake up to 400 mg a day, in the no-concern range for healthy adults.2,8,9,10,11,12

  • Pregnancy, children and teenagers have lower figures

    EFSA's caffeine figures drop to 200 mg a day in pregnancy and 3 mg per kilogram of body weight for under-18s. Soda rarely threatens either — a can of Coke is 34 mg — but a single 12 fl oz Celsius is 200 mg, which is the whole pregnancy figure in one drink.12,11

  • Flat soda is not a treatment for being ill

    Nothing on this page tested people who were ill. For fluid lost to vomiting or diarrhoea, an oral rehydration solution is the drink designed for the job, and WHO's diarrhoea manual lists commercial carbonated drinks among the sugary drinks to avoid, because they can make diarrhoea worse. Symptoms that persist are a reason to talk to a clinician rather than open another can.13

  • If a clinician has capped your fluid, this page does not apply

    Heart failure, kidney disease and some medications come with a fluid limit, and in that situation the volume of a drink matters far more than what is dissolved in it. Follow the number you were given rather than anything derived from a study in healthy young men.

Doesn't a study say soda makes dehydration worse?

  • What the rats went through

    The study behind that claim, García-Arroyo 2016, kept rats in a 36°C chamber for an hour a day, five days a week for four weeks; each session cost them about 1.7% of their body weight. For two hours afterwards they drank water, an 11% fructose-glucose solution made to match a soft drink's sugar, or stevia-sweetened water, six or seven rats to a group.14

  • What it found

    The sugar-water rats drank more in those two hours, yet ended the month with more concentrated blood and urine, more copeptin (a marker of the water-conserving hormone vasopressin), lower creatinine clearance and more signs of kidney injury than the rats given water. The authors conclude that soft drink-like beverages worsen dehydration.14

  • Why it does not describe a can of Coke

    Rats, not people; a month of repeated heat dehydration, not a rested person with a can; and sugar dissolved in water, with no caffeine, carbonation or cola in it. The authors also report that rats given a similar amount of the sugar drink without the heat showed no kidney changes. The study asks how kidneys cope when sugar water is the recovery drink after dehydration, not how much of a drink a hydrated person keeps, which is what the index above measures.14

  • The human trial that followed

    Chapman 2019 had 12 healthy adults exercise for 4 hours in 35°C heat on two visits, drinking 2 litres of a high-fructose, caffeinated soft drink on one and 2 litres of water on the other, plus at least another litre of the same drink afterwards. After the soft drink, 75% had a rise in blood creatinine that meets the threshold for stage 1 acute kidney injury, against 8% after water. For hard physical work in the heat, that is a reason to drink water rather than soda; it says nothing about a can with lunch.15

Composition

How much water is in a can of soda?

Cola, diet cola, a Sprite-style lemon-lime soda and ginger ale on one scale, with still water as the baseline. Switch the serving to the can or bottle you actually drink.

Serving size

Showing 355 mL · 12 fl oz of each.

Composition of four sodas and still water per 355 mL serving, from USDA FoodData Central
DrinkWaterby weightWater in itper servingCaloriesSugarsProteinSodiumPotassiumCalcium
Cola89.4%332mL11.2 fl oz156kcal37g0g11mg19mg4mg
Diet cola99.5%358mL12.1 fl oz7kcal0g0.4g29mg29mg11mg
Lemon-lime soda89.5%329mL11.1 fl oz151kcal38.2g0.3g37mg4mg7mg
Ginger ale91.2%339mL11.5 fl oz126kcal33.1g0g26mg4mg11mg
Still water, for comparison99.9%360mL12.2 fl oz0kcal0g0g14mg0mg11mg

USDA publishes composition per 100 grams, so each serving is converted through the item's own density — about 1.0482 g/mL for cola and ginger ale and 1.0144 g/mL for diet cola and water, each derived by USDA from that item's own 12 fl oz portion weight. Those weights are rounded household conventions, so treat the densities as good to a couple of percent. Water mass is shown as millilitres on the basis that 1 g of water is 1 mL. These are generic USDA drinks rather than any one label: USDA's cola gives 156 calories and 37 g of sugars per 12 fl oz where Coca-Cola's own FAQ gives 140 and 39 g. Either way, roughly nine to ten teaspoons of sugar.7

Which USDA entries these are
  • Cola: Soft drink, cola — FDC 2710541, Food and Nutrient Database for Dietary Studies (FNDDS) 2024-10-31
  • Diet cola: Soft drink, cola, diet — FDC 2710542, Food and Nutrient Database for Dietary Studies (FNDDS) 2024-10-31
  • Lemon-lime soda: Beverages, carbonated, lemon-lime soda, no caffeine — FDC 173205, SR Legacy 2018-04
  • Ginger ale: Soft drink, ginger ale — FDC 2710555, Food and Nutrient Database for Dietary Studies (FNDDS) 2024-10-31
  • Still water, for comparison: Water, tap — FDC 2710707, Food and Nutrient Database for Dietary Studies (FNDDS) 2024-10-31

Why the diet cola and water rows read a shade high

Run the arithmetic and a 12 fl oz can of diet cola returns about 358 mL of water — more than the can holds — because USDA's density comes from a rounded household portion weight (see the note under the table). Read those two rows as "essentially all of it": a diet cola is 99.5% water and delivers, at most, the volume you poured. The cola row has no such problem: at 89.4% water it delivers about 332 mL (11.2 fl oz) from a 12 fl oz can, against roughly 355 mL from a glass of water the same size.7

Your can

How much of your daily water does a soda cover?

Pick a soda and a size to see the water it carries, the calories and sugar that come with it, and where it lands against your daily goal.

mL

355 mL · 12 fl oz

mL

68 fl oz. Not sure? The intake calculator works it out from your weight.

355 mL of cola delivers

332mL of water

11.2 fl oz · 89.4% water by weight

Share of your goal16.6%

Counted as volume rather than water content, it is 17.7% of the goal, which is how Water Goose logs it: the whole glass, with no hydration multiplier. The guidance is making a narrower point: EFSA and NASEM both count the water a drink carries toward your total intake — the water in it, rather than the volume of the glass.16,17

Calories
156kcal
Sugars
37g
Protein
0g
Sodium
11mg
Potassium
19mg
Calcium
4mg

In Water Goose this logs as Soda at full volume — the app counts the whole can, and this page is the explanation of why that is a fair way to count it.

Composition from USDA FoodData Central, converted through each drink’s density.7 Work out your daily goal

What this calculator leaves out

The caffeine. A 12 fl oz cola carries 33 mg by USDA's figures, or 34 mg by Coca-Cola's own. The caffeine calculator in the tools below adds it up across everything else you drank.7,2

Questions

Does Diet Coke, Sprite or Celsius hydrate you?

Does Coke count toward your daily water intake?

Yes. Coke is about 89% water, so a 12 fl oz can carries roughly 332 mL of fluid, and in the trial that created the beverage hydration index cola held on to fluid no differently from still water over the two hours after drinking. That is the science. Separately, Water Goose logs a can at its full volume, with no hydration multiplier, like every other drink in the app.7,1

Is 2 Cokes a day too much?

On caffeine, no. On sugar, it is more than WHO's limit for a whole day. Two 12 fl oz cans of Coke are 68 mg of caffeine, well inside the 400 mg a day EFSA treats as no concern for healthy adults and the 200 mg it sets for pregnancy. They are also 78 g of sugar and 280 calories, against WHO's upper limit for free sugars of about 50 g a day on a 2,000-calorie diet. Diet Coke or Coke Zero drops the sugar, not the caffeine.2,4,12,18

Does Diet Coke hydrate you?

Yes. Diet Coke is about as hydrating as a soft drink gets: 99.5% water by USDA's figures, no sugar, and 43 mg of caffeine per 12 fl oz by those same figures or 46 mg by the label. In the index trial diet cola scored 1.08, which was not significantly different from still water.7,8,1

Does Coke Zero hydrate you?

Very likely as well as Diet Coke, though no trial has tested it. Its label is close to Diet Coke's: zero calories, zero sugar, 40 mg of sodium and 34 mg of caffeine in a 12 fl oz can, plus 60 mg of potassium. Nothing in that list would be expected to behave differently from the diet cola that was measured.19,1

Does Sprite hydrate you?

Yes. Sprite is hydrating, and unlike cola it has no caffeine at all. USDA's lemon-lime soda is 89.5% water, so a 12 fl oz serving carries about 329 mL of fluid along with 38.2 g of sugars; a can of Sprite lists 38 g. No hydration trial has tested Sprite itself. Its measured osmolality, 479 to 556 mOsm/kg against blood's 275-295, comes from the sugar, not the bubbles.7,5,20,21

Is ginger ale hydrating?

Yes, and it is the mildest of the group: 91.2% water, about 339 mL of fluid and 33.1 g of sugars per 12 fl oz, and no caffeine. Schweppes ginger ale measured 497 mOsm/kg in a Swiss survey. No hydration trial has tested it. It is not a remedy for a stomach bug: WHO's diarrhoea manual lists commercial carbonated drinks among the sugary drinks to avoid, and an oral rehydration solution is the drink designed for that job.7,20,13

Does Celsius hydrate you?

Less well than water, in the one trial that tested it. Adults who drank 500 mL of Celsius Live Fit — 280 mg of caffeine and almost no sodium — plus 500 mL of water had a hydration index of 0.86 four hours later, significantly below water's 1.00. A 12 fl oz can of Celsius Sparkling Orange lists 200 mg of caffeine, about six cans of Coke. The trial was funded by Liquid I.V., whose own drink matched water.22,11,2

Does soda hydrate you as fast as water?

No trial on this page timed how fast a drink hydrates you, and what is known gives regular soda no head start. Cola in the index trial was 10.6% carbohydrate, above the 3-8% NATA gives as best for fluid absorption when a drink contains carbohydrate, and concentrated sugar slows the stomach: a 188 g/L glucose drink took 130 minutes to half-empty, against 17 for a 40 g/L one. Over the two hours after drinking, cola held on to fluid no differently from still water. If you are losing fluid to illness, an oral rehydration solution is the drink designed for it.1,23,24,13

What drink hydrates you fastest? Every drink compared

Can the caffeine in cola pull out more fluid than the drink puts in?

Not at these doses. A measurable diuretic effect needs roughly 250-300 mg of caffeine in one go, and a 12 fl oz can of Coke has 34 mg. When the same research group varied caffeine from 0 to 400 mg per litre while holding everything else steady, urine output did not change.3,2,25

Can you drink soda instead of water?

For fluid, largely yes: cola is about 89% water and held fluid like water in the index trial. For everything else, no. A single can of Coke is 39 g of sugar and 140 calories, against WHO's limit of about 50 g of free sugars for the whole day. Soda counts toward your intake; water does the same job without the sugar.7,1,4,18

The rest of the evidence

Is there more evidence than one trial?

Maughan 2016 is the only trial that has measured how much of a cola people keep, and this page is not going to pretend otherwise. The studies below were each run a different way, so none of them shares a scale with the index above: one takes a soft drink's recipe apart ingredient by ingredient, one shows where the fluid from a sugary drink actually is two hours later, one tests the bubbles, and one tests the energy drinks people line up next to soda.

  • At restHydration index

    Sugar and salt changed how much fluid people kept; caffeine up to 400 mg per litre did not (Maughan 2019)

    25

    Retention rose with sucrose (10-20%) and sodium (27-52 mmol/L); caffeine up to 400 mg/L had no effect.

    Method, results and caveats

    3 separate cohorts of 12 young active men. Double-blind crossover; 1 L of drink; 4-h urine collection; BHI and net fluid balance.

    What each group drank in Maughan 2019, and what was measured
    Sucrose 0, 5, 10 and 20%10% and 20% sucrose gave lower urine output and higher net fluid balance than 0% and 5%.
    Sodium 7, 15, 27 and 52 mmol/L27 and 52 mmol/L gave greater retention and BHI than 7 and 15 mmol/L.
    Caffeine 0-400 mg/LNo effect of caffeine on urine output (p=0.83), and no differences in arginine vasopressin or aldosterone.
    • — Abstract only; no numeric BHI values.
    • — Peden 2024 describes the sucrose result as only the 20% drink raising BHI, which conflicts with this abstract.
  • After exerciseFluid retainedDifferent protocol

    Part of a sugary drink's apparent retention was fluid still sitting in the stomach (Clayton 2014)

    26

    The 10% drink's higher apparent retention partly reflected fluid still in the stomach; once that was accounted for, the 2% drink gave the better net fluid balance at 60 and 120 min.

    Method, results and caveats

    8 people. About 1.8% body-mass loss; drank 150% of the loss; gastric contents sampled to 120 min.

    What each group drank in Clayton 2014, and what was measured
    2% glucose-electrolyte drink0.3% of the drink left in the stomach at 120 min; 52% retained at 240 min.
    10% glucose-electrolyte drink42.1% of the drink left in the stomach at 120 min (p<.001); 64% retained at 240 min.
    • — Abstract only.
  • Mildly dehydratedFluid retainedDifferent protocol

    Bubbles did not help people keep fluid; added sodium did (Takamata 2026)

    27

    Adding sodium increased retention; carbonation did not improve it.

    Method, results, caveats and funding

    Stomach discomfort was higher with both carbonated drinks than with still electrolyte water (p=0.019 and p=0.004).

    15 adults (8 women, 7 men). Drinking freely for 180 min after about 1% body-mass loss; urine in g per kg body mass.

    What each group drank in Takamata 2026, and what was measured
    WaterreferenceUrine 7.56 ± 1.61 g/kg; retention 53.7 ± 5.9%. Cumulative intake was greatest with plain water.
    Carbonated waterUrine 6.22 ± 1.01 g/kg; retention 42.5 ± 6.9%.
    Electrolyte waterUrine 3.21 ± 0.58 g/kg; retention 68.3 ± 3.5%.
    Carbonated electrolyte waterUrine 3.66 ± 0.68 g/kg; retention 68.8 ± 4.5%.
    • — Free drinking, so volumes differ between drinks.
    • — Funded by ITO EN, Ltd.; seven of thirteen authors are employees.

    Funding: Funded by ITO EN, Ltd.; seven of the thirteen authors are ITO EN employees.

  • At restHydration indexDifferent protocol

    Two 280 mg energy drinks held less fluid than water; a 106 mg drink with electrolytes matched it (Millard-Stafford 2025)

    22

    The two low-sodium drinks with 280 mg caffeine retained less fluid than water at 4 h; the lower-caffeine drink with electrolytes and carbohydrate matched water.

    Method, results, caveats and funding

    Habitual caffeine use made no difference (0.92 ± 0.1 vs 0.93 ± 0.1, p=0.827). Women had a higher BHI than men with the caffeinated drinks (reported as +0.077, p=0.043; the abstract gives p=0.03).

    28 adults (14 men, 14 women); caffeine 3.7 ± 0.4 mg/kg in men and 4.8 ± 0.8 mg/kg in women. Randomised crossover; 250 mL water, 500 mL test drink, then 250 mL water, in four portions over 30 min; 240 min. Composition measured per 500 mL.

    What each group drank in Millard-Stafford 2025, and what was measured
    Waterreference% retained at 240 min -48.2 ± 3.8
    Caffeinated energy drink (CAF)Celsius Live Fit, mango passionfruit (carbonated)0.86 (SD 0.16) at 240 minUrine 244 g more than CAF+CE. % retained -71.2 ± 21.5.
    Caffeinated energy drink with electrolytes (CAF+E)Prime Energy, orange mango0.91 (SD 0.16) at 240 minUrine 162 g more than CAF+CE. % retained -65.1 ± 26.3.
    Caffeinated carbohydrate-electrolyte mix (CAF+CE)Liquid I.V. Energy Multiplier, mango tamarind, in 500 mL water1.01 (SD 0.12) at 240 min% retained -46.4 ± 18.8.
    • — Not the standard protocol: only 500 mL of test drink, so values are not comparable with 1-L BHI studies.
    • — Funded by Liquid I.V. (Unilever), maker of the drink that matched water.
    • — High caffeine per kg of body mass.

    Funding: Funded by Liquid-IV, a Unilever company (grant GR00027334), maker of the Liquid I.V. Energy Multiplier that matched water in the trial. A Liquid IV principal scientist helped conceptualise and review the manuscript. The first author has also had funding from Coca-Cola, Kraft and Liquid IV.

Three more lines of evidence, each on a protocol of its own

  • Grandjean 2000: over a day, the differences wash out

    Eighteen men drank combinations of water, caffeinated and non-caffeinated colas and coffee. There were no differences in body weight or in the blood and urine markers of hydration.28

  • Zhang 2015: caffeine's diuresis is small and disappears with exercise

    Sixteen studies, 28 effect sizes, 379 people, at a median dose of 300 mg — nine times a can of Coke. At rest that produced about 120 mL more urine (effect size 0.54); during exercise there was no effect at all (0.10, P = 0.248).29

  • Killer 2014: three days of coffee matched three days of water

    Fifty habitual coffee drinkers took about 308 mg of caffeine a day as coffee for three days. Total body water and 24-hour urine were no different from the same volume of water. The trial was funded by a coffee-industry science institute, which is named in the references.30

Mechanism

What do the sugar, caffeine and bubbles actually do?

A soda is a sugar solution with a little caffeine in it and gas dissolved in the top. Each of those three does something measurable, and the one people worry about — the caffeine — is the one doing the least.

  • Moderate evidenceReview

    Large single doses of caffeine briefly raise urine output, but mainly in people who have gone without caffeine for days or weeks. The caffeine in standard servings of tea, coffee and soft drinks appears to have no diuretic action.3

    At least 250-300 mg of caffeine, which the review equates to 2-3 cups of coffee or 5-8 cups of tea. Literature searched from January 1966 to March 2002.

    Caveat: Abstract only; the full text is paywalled.

  • Moderate evidenceRandomised trial

    Both carbohydrate content and osmolality slow how fast a drink leaves the stomach, and carbohydrate content matters more. A concentrated glucose drink took several times longer to empty than a dilute one.24

    600 mL test drinks, n=6. Half-emptying time: 40 g/L glucose (230 mosmol/kg) 17 ± 1 min; 40 g/L glucose polymer (42 mosmol/kg) 14 ± 1 min; 188 g/L glucose polymer (237 mosmol/kg) 64 ± 8 min; 188 g/L glucose (1300 mosmol/kg) 130 ± 18 min. Values are mean ± SEM.

    Caveat: Abstract only. 188 g/L is about 18.8% carbohydrate, roughly twice a typical cola.

  • Moderate evidenceRandomised trial

    After exercise, a hypertonic 10% glucose drink left much more fluid sitting in the stomach than a 2% drink, which explains part of its lower early urine output.26

    n=8, about 1.8% body mass lost, drank 150% of the loss. At 120 min, 0.3% of the 2% drink and 42.1% of the 10% drink remained in the stomach (p<.001). Retained at 240 min 52% vs 64%. Once gastric residue was accounted for, net fluid balance was better with the 2% drink at 60 and 120 min.

    Caveat: Abstract only.

  • Moderate evidenceRandomised trial

    Measured composition of 13 common drinks shows the sugary ones are far more concentrated than milk or the sports drink, which sit near the osmolality of the participants' own blood.1

    Osmolality in mmol/kg, Na and K in mmol/L: still water 2 (Na 0); sparkling water 7 (Na 1); cola 432 (carbohydrate 10.6 g/100 mL, Na 2, caffeine 96 mg/L); diet cola 23 (caffeine 127 mg/L); sports drink 297 (3.9 g/100 mL, Na 21, K 4); ORS 229 (1.8 g/100 mL, Na 55, K 20); orange juice 570 (10.5 g/100 mL, Na 1, K 33); lager 774 (2.2 g/100 mL); coffee 34 (caffeine 212 mg/L); hot tea 16 and cold tea 18 (caffeine 179 mg/L); full-fat milk 286 (Na 18, K 41); skimmed milk 282 (Na 19, K 40). Participants' baseline serum osmolality was 293 (6) mmol/kg.

    Caveat: Single UK commercial products from 2014; brands vary. The 275-295 mOsm/kg range often attached to this table is not in the paper: it comes from Sadowska 2017.

  • Strong evidenceGuideline

    NATA says the optimal carbohydrate concentration for fluid absorption is 3-8%, and that more than 5-8% may slow it.23

    Carbohydrate 3-8% optimal; above 5-8% may slow absorption; 400-600 mL in the stomach works best; about 200 mL every 15-20 min; exercise above 80% VO2max may slow gastric emptying.

  • Moderate evidenceRandomised trial

    At a fixed 1 L volume, sparkling water produced the same urine output over 4 h as still water, so carbonation itself did not change fluid retention.1

    Sparkling water osmolality 7 mmol/kg, Na 1 mmol/L; cumulative 4-h urine not different from still water.

How concentrated these drinks actually are

Osmolality is what decides how fast a drink leaves the stomach and how water moves in the gut. Blood sits at roughly 275–295 mOsm/kg21. Drinks near that range empty quickly; concentrated ones sit far above it.

Measured osmolality of the drinks on this page
DrinkOsmolalitySpreadn
Soft drinks31Sugar 8.7 g/dL; pH 3.1.693mOsm/L——
Soda20Dr Pepper646mOsm/kg——
Cola, regular21Coca-Cola (label sugar 10.6%)632mOsm/kgSD 1.53—
Bitter lemon20Schweppes627mOsm/kg——
Cola, dark, regular32614.8mOsm/kgSD 87.435
Lemon-lime soda21Sprite (sugar 10.6%)556mOsm/kgSD 2.31—
Orangeade21Sugar 8.6%551mOsm/kgSD 4.16—
Tonic water20Schweppes501mOsm/kg——
Clear cola ('colas blancas'), regular32Reading 'colas blancas' as lemon-lime type is an interpretation, not the paper's definition.497.8mOsm/kgSD 98.535
Ginger ale20Schweppes497mOsm/kg——
Cola, regular20Coca-Cola (10.6 g carbohydrate/100 g, pH 2.4)493mOsm/kg——
Cola, regular21Pepsi (label sugar 11%)492mOsm/kgSD 3.21—
Lemon-lime soda20Sprite479mOsm/kg——
Orange soda20Fanta415mOsm/kg——
Cola, dark, low-calorie3262.6mOsm/kgSD 9.520
Clear cola, low-calorie3260.8mOsm/kgSD 10.320
Diet cola21Pepsi light34mOsm/kgSD 1.73—
Diet cola21Coca-Cola light29mOsm/kgSD 4.73—
Diet cola20Coca-Cola light27mOsm/kg——
Diet cola20Pepsi max27mOsm/kg——
Diet cola20Pepsi light25mOsm/kg——

The bubbles change how it feels, not how it counts

Sparkling water scored 0.98 in the same trial, no different from still water, so carbonation on its own does not move retention. What it moves is behaviour: heavily carbonated drinks were rated less thirst-quenching and people chose to drink less of them after exercise, and carbonated water raised short-term fullness in a separate trial. The sparkling water post linked below takes that question on its own.1,33,34

Should You Worry About Caffeine Dehydrating You?

SciShow · starts at 0:10 · Watch on YouTube

SciShow explains why it is so hard to test whether caffeine dehydrates you, and where the belief may have started. It is mostly about coffee, but it ends where this page does: a few caffeinated sodas will not dehydrate you, and hydration is not the reason to cut back on them.

Nothing loads from YouTube until you press play.

Labels

How much caffeine and sugar is in Coke, Diet Coke and Sprite?

Label panels for the cans people actually buy, with two energy drinks at the bottom as a caffeine comparison. These are label values for one flavour and size, not laboratory measurements, and none of the brands here had any involvement in this page.

Published nutrition panels for branded products, per the serving each label states
ProductServingCaloriesSugarsProteinSodiumPotassium
Coca-Cola4Coca-Cola Original, 12 fl oz can12 fl oz can14039 g———
Coca-Cola4Coca-Cola Original, 20 fl oz bottle1 bottle (20 fl oz)24065 g—75 mg—
Coca-Cola8Diet Coke, 12 fl oz can1 can (12 fl oz)00 g—40 mg—
Coca-Cola19Coca-Cola Zero Sugar, 12 fl oz can1 can (12 fl oz)00 g—40 mg60 mg
Sprite5Sprite (original lemon-lime), 12 fl oz can1 can (12 fl oz)14038 g—65 mg—
Red Bull9Red Bull Energy Drink, 8.4 fl oz can8.4 fl oz11026 g0 g105 mg—
Red Bull10Red Bull Energy Drink, 12 fl oz can12 fl oz—————
CELSIUS11Sparkling Orange, 12 fl oz can12 fl oz (355 mL)10——5 mg—

Labels checked 2026-09-15. A dash means the label does not publish that value — it is not a zero. Formulations and panels change, so treat these as a snapshot and check the carton in your hand.

  • Coca-Cola Original, 12 fl oz can: From the product page FAQ, not a nutrition panel; sodium per 12 oz is not given.
  • Coca-Cola Original, 12 fl oz can: The caffeine FAQ gives the same 34 mg for a 12-oz can.
  • Coca-Cola Original, 12 fl oz can: Caffeine 34 mg per 12 fl oz can.
  • Coca-Cola Original, 20 fl oz bottle: 65 g added sugars.
  • Coca-Cola Original, 20 fl oz bottle: Caffeine is listed as an ingredient but not stated per 20 fl oz.
  • Coca-Cola Diet Coke, 12 fl oz can: Sweetened with aspartame; contains phenylalanine.
  • Coca-Cola Diet Coke, 12 fl oz can: Caffeine 46 mg per 1 can (12 fl oz).
  • Coca-Cola Zero Sugar, 12 fl oz can: Sweetened with aspartame, acesulfame potassium and stevia extract.
  • Coca-Cola Zero Sugar, 12 fl oz can: Caffeine 34 mg per 1 can (12 fl oz).
  • Sprite (original lemon-lime), 12 fl oz can: 38 g added sugars.
  • Sprite (original lemon-lime), 12 fl oz can: Label says 'no caffeine'.
  • Sprite (original lemon-lime), 12 fl oz can: Caffeine 0 mg per 1 can (12 fl oz).
  • Red Bull Energy Drink, 8.4 fl oz can: Sugar from the formal nutrition declaration; the same page's body text says 27 g.
  • Red Bull Energy Drink, 8.4 fl oz can: Caffeine 80 mg per 8.4 fl oz.
  • Red Bull Energy Drink, 8.4 fl oz can: Listed here only as a caffeine comparison. It is not a soda, and nothing on this page treats it as a way to hydrate.
  • Red Bull Energy Drink, 12 fl oz can: Caffeine 114 mg per 12 fl oz.
  • Red Bull Energy Drink, 12 fl oz can: Listed here only as a caffeine comparison. It is not a soda, and nothing on this page treats it as a way to hydrate.
  • CELSIUS Sparkling Orange, 12 fl oz can: The label prints carbohydrate as '0mg' and calls the drink 'not a significant source' of sugars and potassium.
  • CELSIUS Sparkling Orange, 12 fl oz can: Caffeine 200 mg per 12 fl oz (355 mL).
  • CELSIUS Sparkling Orange, 12 fl oz can: Listed here only as a caffeine comparison. It is not a soda, and nothing on this page treats it as a way to hydrate.

Caffeine, side by side

  • Coca-Cola, 12 fl oz: 34 mg

    The brand's own caffeine FAQ gives 34 mg for a 12-ounce can of Coke and 46 mg for Diet Coke — the diet version has the most of the two.2,8

  • Coca-Cola Zero Sugar: 34 mg

    The same as Original in a 12 fl oz can, with 0 calories, 0 g of sugar, 40 mg of sodium and 60 mg of potassium.19

  • Sprite: none

    The label says no caffeine, and USDA's generic lemon-lime soda agrees at 0 mg. The 38 g of sugar in a can is the part worth noticing.5,7

  • Red Bull: 80 mg, or 114 mg in a 12 fl oz can

    Roughly two to three cans of Coke in one drink. Not a soda, and not something this page treats as a way to hydrate.9,10

  • Celsius Sparkling Orange: 200 mg

    About six cans of Coke's worth in one 12 fl oz can. A different Celsius line scored 0.86 against water in the 2025 energy-drink trial above.11

Receipts

Where every number on this page comes from

Where the composition comes from

U.S. Department of Agriculture, Agricultural Research Service. FoodData Central. Built 2026-09-15 from the published CSV releases, never hand-typed.

  • Food and Nutrient Database for Dietary Studies (FNDDS) · 2024-10-31
  • SR Legacy · 2018-04
  • — Drinks and prepared foods use FNDDS (foods and drinks as consumed) whenever FNDDS has a code for the item.
  • — Raw produce and dairy foods use Foundation Foods when the entry is current (listed in foundation_food.csv), stands for the food generally rather than one cultivar or colour, and reports water, energy and potassium, plus fiber for plant foods. Otherwise SR Legacy.
  • — A Foundation pick with no household portions uses the portions of the SR Legacy entry for the same food (portionsSource).
  • — Fluid milks use FNDDS, whose composition matches the Foundation analyses (crossCheck) and which has consistent drink portions.
  • — SR Legacy fills any remaining gap. No proxy is used where USDA has no sensible entry (see missing).

What this evidence cannot tell you

  • — The Beverage Hydration Index measures short-term retention, not 24-h hydration: for each person it is urine after still water divided by urine after the test drink, anchored 2 h after drinking 1 L over 30 min.
  • — Most participants were young, healthy, euhydrated, fasted, rested men given a single 1 L dose. Older adults retain more water and respond differently.
  • — Post-exercise retention percentages come from dehydrated people drinking 100-150% of the body mass they lost. They are not comparable to BHI values and must not share a scale with them.
  • — Clarke 2019 reports mean ± SEM while most studies report SD, so spreads are not directly comparable.
  • — No resting BHI data were found for soup, smoothie, lemonade or coconut water. Energy-drink evidence comes from one modified-protocol study. The only hydration-index data for soda are cola and diet cola in Maughan 2016; the other soda studies cited (Grandjean 2000 over a day, Chapman 2019 during exercise in heat, García-Arroyo 2016 in rats) measured different outcomes.
  • — Many of these studies are industry funded: the European Hydration Institute, Entrinsic, Dairy Management, Nuun, Coca-Cola, Buoy, Lingtea, QCK, the Almond Board, 8 POiNT, VitaCoco, Liquid I.V., Innate-Essence, ITO EN, the Dutch Beer Institute, the Centro de Información Cerveza y Salud and ISIC all appear as funders.
  • — Commercial formulations change over time. Compositions are as measured or labelled at the time of each study and are not current labels.

Who paid for the research

Hydration research is heavily industry funded. That does not make a study wrong, but you should know who paid before you weigh it. Water Goose took no money from anyone named here, and no brand saw this page before it went up.

  • — Maughan 2016: Funded by a grant from the European Hydration Institute (EHI). Prof Maughan chairs the EHI Scientific Advisory Board (not the Institute itself); Dr Watson has also received EHI funding.
  • — García-Arroyo 2016: Funded by CONACyT Mexico and the Instituto Nacional de Cardiología Ignacio Chávez. Two authors (Johnson, Lanaspa) are named inventors on patent applications for blocking fructose metabolism to prevent kidney disease; Johnson also has funding from Amway and sits on its Scientific Board, and three authors hold grants from Danone; Johnson, Roncal-Jiménez and Sánchez-Lozada are members of Colorado Research Partners.
  • — Millard-Stafford 2025: Funded by Liquid-IV, a Unilever company (grant GR00027334), maker of the Liquid I.V. Energy Multiplier that matched water in the trial. A Liquid IV principal scientist helped conceptualise and review the manuscript. The first author has also had funding from Coca-Cola, Kraft and Liquid IV.
  • — Takamata 2026: Funded by ITO EN, Ltd.; seven of the thirteen authors are ITO EN employees.
  • — Killer 2014: Funded by ISIC.
  • — Passe 1997: Authors affiliated with the Gatorade Sports Science Institute, Barrington, IL.

References

Every number on this page points at one of these. Product labels were checked 2026-09-15.

  1. 1

    Maughan RJ, Watson P, Cordery PAA, Walsh NP, Oliver SJ, Dolci A, Rodriguez-Sanchez N, Galloway SDR. A randomized trial to assess the potential of different beverages to affect hydration status: development of a beverage hydration index. Am J Clin Nutr 2016;103(3):717-723.

    StudyRead: full textOpen source

    Funding: Funded by a grant from the European Hydration Institute (EHI). Prof Maughan chairs the EHI Scientific Advisory Board (not the Institute itself); Dr Watson has also received EHI funding.

    Read from the LJMU green open-access accepted manuscript (https://researchonline.ljmu.ac.uk/id/eprint/12468/); the publisher page was blocked. ISRCTN13014105.

  2. 2

    Coca-Cola US. What is caffeine? (FAQ).

    Product labelRead: official pageOpen source

  3. 3

    Maughan RJ, Griffin J. Caffeine ingestion and fluid balance: a review. J Hum Nutr Diet 2003;16(6):411-420.

    StudyRead: abstractOpen source

    Narrative review; the source of Maughan 2016's 250-300 mg threshold.

  4. 4

    Coca-Cola US. Coca-Cola Original product page, nutrition facts and FAQ.

    Product labelRead: official pageOpen source

    The only 12 fl oz panel on this page belongs to Coca-Cola Caffeine Free; 12 oz figures for Original come from the page FAQ.

  5. 5

    Coca-Cola US. Sprite products, nutrition facts.

    Product labelRead: official pageOpen source

  6. 6

    Centers for Disease Control and Prevention. Water and Healthier Drinks. Last reviewed 5 March 2026.

    GuidelineRead: official pageOpen source

    Read through a summarising fetch tool; do a verbatim check before quoting its wording.

  7. 7

    U.S. Department of Agriculture, Agricultural Research Service. FoodData Central (SR Legacy and Foundation Foods).

    DatasetRead: official pageOpen source

    Water content is not the same thing as a net hydration effect.

  8. 8

    Coca-Cola US. Diet Coke products, nutrition facts.

    Product labelRead: official pageOpen source

  9. 9

    Red Bull US. Red Bull Energy Drink ingredients list and nutrition declaration (8.4 fl oz).

    Product labelRead: official pageOpen source

    The page body says 27 g sugars; its formal declaration and comparison graphic say 26 g. brands.ts uses the declaration.

  10. 10

    Red Bull US. How much caffeine is in a can of Red Bull Energy Drink?

    Product labelRead: official pageOpen source

  11. 11

    CELSIUS. Sparkling Orange, 12 fl oz can label and Essential Facts FAQ.

    Product labelRead: official pageOpen source

  12. 12

    EFSA NDA Panel. Scientific Opinion on the safety of caffeine. EFSA Journal 2015;13(5):4102.

    GuidelineRead: official pageOpen source

    Figures are from EFSA's caffeine topic page; the full opinion returned 403. These are safety limits, not hydration thresholds.

  13. 13

    World Health Organization. The treatment of diarrhoea: a manual for physicians and other senior health workers, 4th revision. Geneva: WHO; 2005.

    GuidelineRead: full textOpen source

  14. 14

    García-Arroyo FE, Cristóbal M, Arellano-Buendía AS, Osorio H, Tapia E, Soto V, Madero M, Lanaspa MA, Roncal-Jiménez C, Bankir L, Johnson RJ, Sánchez-Lozada LG. Rehydration with soft drink-like beverages exacerbates dehydration and worsens dehydration-associated renal injury. Am J Physiol Regul Integr Comp Physiol 2016;311(1):R57-R65.

    StudyRead: full textOpen source

    Funding: Funded by CONACyT Mexico and the Instituto Nacional de Cardiología Ignacio Chávez. Two authors (Johnson, Lanaspa) are named inventors on patent applications for blocking fructose metabolism to prevent kidney disease; Johnson also has funding from Amway and sits on its Scientific Board, and three authors hold grants from Danone; Johnson, Roncal-Jiménez and Sánchez-Lozada are members of Colorado Research Partners.

    Animal study in male Wistar rats: 36°C for 1 h a day, Monday to Friday for 4 weeks (1.7% body-weight loss each time), then 2 h to drink tap water (n = 6), 11% fructose-glucose (7.15% fructose, 3.85% glucose; n = 7) or stevia water (n = 7); 5 unheated controls. The test drink was sugar in water, not a commercial soft drink: no caffeine, carbonation or acid. The authors report that rats given a similar amount of the sugar drink without heat showed no renal changes (data not shown), and that the creatinine-clearance difference could partly reflect renal handling of creatinine.

  15. 15

    Chapman CL, Johnson BD, Sackett JR, Parker MD, Schlader ZJ. Soft drink consumption during and following exercise in the heat elevates biomarkers of acute kidney injury. Am J Physiol Regul Integr Comp Physiol 2019;316(3):R189-R198.

    StudyRead: abstractOpen source

    Full text blocked by the publisher's bot check, so only the abstract is used: 12 healthy adults, counterbalanced soft-drink and water trials, 2 L during 4 h of exercise at 35.1°C and at least 1 L after. The accompanying editorial (Sánchez-Lozada et al. 2019, PMC6459378) names the drink as Mountain Dew; the page does not.

  16. 16

    EFSA Panel on Dietetic Products, Nutrition, and Allergies (NDA). Scientific Opinion on Dietary Reference Values for water. EFSA Journal 2010;8(3):1459.

    GuidelineRead: full textOpen source

    Read from the DTU Orbit copy of the published PDF; Wiley was blocked.

  17. 17

    Institute of Medicine. Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate. Chapter 4: Water. Washington, DC: The National Academies Press; 2005.

    GuidelineRead: full textOpen source

    Cite this directly for adequate intakes: Maughan 2016's introduction misstates the women's figure. On alcohol it concludes the diuresis is transient; it makes no explicit 'all drinks count equally' statement.

  18. 18

    World Health Organization. Healthy diet (fact sheet). 26 January 2026.

    GuidelineRead: official pageOpen source

    Free sugars should stay below 10% of total daily energy, which the fact sheet equates to 50 g (about 12 level teaspoons) for a person of healthy body weight eating about 2,000 calories a day. The limit comes from WHO's 2015 guideline on sugars intake for adults and children.

  19. 19

    Coca-Cola US. Coca-Cola Zero Sugar, nutrition facts.

    Product labelRead: official pageOpen source

  20. 20

    Mettler S, Rusch C, Colombani PC. Osmolality and pH of sport and other drinks available in Switzerland. Schweiz Z Sportmed Sporttraumatol 2006;54(3):92-95.

    StudyRead: full textOpen source

    Products bought November 2005; freezing-point osmometer, duplicate readings.

  21. 21

    Sadowska A, Świderski F, Rakowska R, Waszkiewicz-Robak B, Żebrowska-Krasuska M, Dybkowska E. Beverage osmolality as a marker for maintaining appropriate body hydration. Rocz Panstw Zakl Hig 2017;68(2):167-173.

    StudyRead: full textOpen source

    Polish market products. This is the source of the 275-295 mOsm/kg range (it describes the isotonic drinks tested), not Maughan 2016.

  22. 22

    Millard-Stafford M, Hack B, Harp A, Smith E. Caffeinated Energy Drink Formulations Differentially Impact Hydration Versus Water: Does Habitual Caffeine Intake or Biological Sex Matter? Nutrients 2025;17(18):2913.

    StudyRead: full textOpen source

    Funding: Funded by Liquid-IV, a Unilever company (grant GR00027334), maker of the Liquid I.V. Energy Multiplier that matched water in the trial. A Liquid IV principal scientist helped conceptualise and review the manuscript. The first author has also had funding from Coca-Cola, Kraft and Liquid IV.

    Modified protocol: 500 mL of test drink plus 500 mL of water, not 1 L of drink.

  23. 23

    McDermott BP, Anderson SA, Armstrong LE, et al. National Athletic Trainers' Association Position Statement: Fluid Replacement for the Physically Active. J Athl Train 2017;52(9):877-895.

    GuidelineRead: full textOpen source

  24. 24

    Vist GE, Maughan RJ. The effect of osmolality and carbohydrate content on the rate of gastric emptying of liquids in man. J Physiol 1995;486(Pt 2):523-531.

    StudyRead: abstractOpen source

    Values are mean ± SEM.

  25. 25

    Maughan RJ, Watson P, Cordery PAA, Walsh NP, Oliver SJ, Dolci A, Rodriguez-Sanchez N, Galloway SDR. Sucrose and sodium but not caffeine content influence the retention of beverages in humans under euhydrated conditions. Int J Sport Nutr Exerc Metab 2019;29(1):51-60.

    StudyRead: abstractOpen source

    Abstract describes a double-blind crossover design. Numeric BHI values are not in the abstract. Peden 2024 describes the sucrose result differently (only the 20% drink raising BHI).

  26. 26

    Clayton DJ, Evans GH, James LJ. Effect of drink carbohydrate content on postexercise gastric emptying, rehydration, and the calculation of net fluid balance. Int J Sport Nutr Exerc Metab 2014;24(1):79-89.

    StudyRead: abstractOpen source

  27. 27

    Takamata A, Kosugi N, Sakagawa N, et al. Effects of Carbonated and Electrolyte-Added Water on Body Fluid Regulation and Ingestive Behavior During Ad Libitum Rehydration Following Mild Hypohydration. Nutrients 2026;18(12):1846.

    StudyRead: full textOpen source

    Funding: Funded by ITO EN, Ltd.; seven of the thirteen authors are ITO EN employees.

  28. 28

    Grandjean AC, Reimers KJ, Bannick KE, Haven MC. The effect of caffeinated, non-caffeinated, caloric and non-caloric beverages on hydration. J Am Coll Nutr 2000;19(5):591-600.

    StudyRead: abstractOpen source

  29. 29

    Zhang Y, Coca A, Casa DJ, Antonio J, Green JM, Bishop PA. Caffeine and diuresis during rest and exercise: a meta-analysis. J Sci Med Sport 2015;18(5):569-574.

    StudyRead: full textOpen source

    Caffeine sources in the pooled studies were mixed: pills, tea, coffee and caffeinated beverages.

  30. 30

    Killer SC, Blannin AK, Jeukendrup AE. No evidence of dehydration with moderate daily coffee intake: a counterbalanced cross-over study in a free-living population. PLoS One 2014;9(1):e84154.

    StudyRead: full textOpen source

    Funding: Funded by ISIC.

  31. 31

    Chavalittamrong B, Pidatcha P, Thavisri U. Electrolytes, sugar, calories, osmolarity and pH of beverages and coconut water. Southeast Asian J Trop Med Public Health 1982;13(3):427-431.

    StudyRead: abstractOpen source

    Values are osmolarity in mOsm/L.

  32. 32

    Dini E, De Abreu J, López E. Osmolalidad de bebidas de consumo frecuente [Osmolality of frequently consumed beverages]. Invest Clin 2004;45(4):323-335.

    StudyRead: full textOpen source

    Venezuelan products, 2002-2003; vapour-pressure osmometer. Its 'natural' fruit drinks are lab blends of pulp diluted with water, not 100% juice (only the orange juice was undiluted).

  33. 33

    Passe DH, Horn M, Murray R. The effects of beverage carbonation on sensory responses and voluntary fluid intake following exercise. Int J Sport Nutr 1997;7(4):286-297.

    StudyRead: abstractOpen source

    Funding: Authors affiliated with the Gatorade Sports Science Institute, Barrington, IL.

  34. 34

    Wakisaka S, Nagai H, Mura E, Matsumoto T, Moritani T, Nagai N. The effects of carbonated water upon gastric and cardiac activities and fullness in healthy young women. J Nutr Sci Vitaminol 2012;58(5):333-338.

    StudyRead: abstractOpen source

How we compiled this

Composition figures come from USDA FoodData Central — FNDDS 2024-10-31 for cola, diet cola, ginger ale and water, SR Legacy 2018-04 for lemon-lime soda — converted to per-serving amounts through each item's USDA density. Hydration index values come from the 2016 trial that defined the index. Nine of the twelve BHI standard deviations, and eight of the twelve means, are only in the figures; they were read from the figure's vector data and match the text values to about 0.01. The chart marks those standard deviations with ≈. The abstract says the BHI was corrected for water content, but the 1.58, 1.54 and 1.50 values are the uncorrected BHI. Brand figures were read from official product pages and checked on 2026-09-15. Where a study had industry funding or an author has a commercial interest, it is named under "Who paid for the research" below. No one paid for or reviewed this page.7,1

This page describes what studies measured in healthy adults. It is general wellness information, not medical advice, diagnosis or treatment. Fluid needs change with health conditions, medication and pregnancy — and some conditions require drinking less. Talk to a clinician about yours.

Keep the number

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