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Measured against water

Does milk hydrate you?

Hydrates — holds more fluid than water for about 2-4 hours

Yes, and for a few hours it hydrates you better than water. Researchers think milk's energy (protein, lactose and, in whole milk, fat) slows how fast it leaves the stomach, and that its sodium and potassium help the body keep the water, so less of it turns into urine. In a trial of 72 men, where 17 drank each milk and everyone drank still water, a litre of skim milk scored 1.58 and whole milk 1.50 on the beverage hydration index against water's 1.00, and both left around a fifth less urine over the next four hours. That helps when you cannot drink again for a while or are replacing sweat after exercise; in an ordinary day your next drink or meal overrides it, and every glass brings calories water does not.1,2,3

Count your glass
Skim milk
1.581
2-hour hydration index; water is 1.00
Whole milk
1.501
2-hour hydration index; water is 1.00
Water in whole milk
88.1%4
A 250 mL glass carries about 227 mL of water
Urine over 4 hours
-22%1
1,049 g after skim milk vs 1,337 g after water

Last reviewed 25 sourcesWritten from the studies, not from other websites

The measurement

Is milk more hydrating than water?

Over the few hours after you drink it, yes. Two hours after a litre, skim milk scored 1.58 and whole milk 1.50 on the beverage hydration index, where water is 1.00 and anything higher means more of the drink stayed in you. Allowing for milk being only 88-91% water trims that to 1.44 and 1.32, still significantly above water. The index is urine after a litre of still water divided by urine after a litre of the test drink; of the 13 drinks tested, only the two milks and the oral rehydration solution stayed above water once that correction was made.

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.
  • — Caffeine at 96-212 mg in these drinks had no effect on net fluid balance. The authors cite a threshold of about 250-300 mg for a measurable diuretic effect (Maughan & Griffin 2003).

Water, coffee, OJ or milk - which one is the best hydrater? - BBC

BBC · starts at 0:44 · Watch on YouTube

Stuart Galloway of the University of Stirling, a co-author of the hydration index study this page is built on, runs a small version of its urine test in a BBC office: six volunteers per drink, a litre of water, orange juice, coffee or semi-skimmed milk, and a pot for every hour. It is a TV demonstration rather than a trial, but he explains plainly why milk holds on to water: its protein slows delivery to the blood, and its sodium and potassium help the body keep it.1

Where the video goes further than the evidence

Near the end the presenter calls milk “the best hydrator” for “sustained all-round hydration” and Galloway agrees, but the studies on this page follow people for a few hours, none compares milk with water across a full day, and the index cannot rank milk above an oral rehydration solution.1

Nothing loads from YouTube until you press play.

The honest part

When is water better than milk?

For everyday drinking, mostly. The measurement above is real but narrow, and these are the places where milk stops being the better answer.

  • Milk brings calories that water does not

    The trial fed everyone a full litre. At USDA's figures that is 629 kcal of whole milk or 351 kcal of skim, against zero for water. A 250 mL glass of whole milk is about 157 kcal. If you are drinking to a daily fluid target, replacing water with milk means drinking your target in food energy too.4,1

  • The advantage lasts hours, not a day

    Every index number here comes from rested, already-hydrated young men who drank a litre in 30 minutes, with urine collected for four hours. The authors anchored the index at two hours partly because in an ordinary day people rarely go longer than that between drinks, and the next drink or meal overrides the last. No study has followed milk against water across 24 hours, and in the one resting milk trial that included older men, milk was retained longer in the young men only.1,5

  • If you are lactose intolerant, the evidence does not cover you

    The post-exercise milk trial excluded people with lactose intolerance by design, and no hydration index study has tested lactose-free milk. Splitting lactose into glucose and galactose raises osmolality: lactose-reduced UHT milk measured 389.1 mOsm/kg against 273-283 for ordinary milk. Undigested lactose pulls water into the gut, and the resulting diarrhoea loses fluid rather than holding it.3,6

  • Plant milks are not covered by any of this

    Oat, soy and almond milk have no beverage hydration index. The one close measurement matched a soy drink and skim milk for water content and found almost identical urine output. Treat the plant-milk rows in the table below as composition, not as evidence of retention.7,4

  • Milk counts, but water is still the sensible default

    The NHS says drinks besides water count toward fluid intake, naming water, lower-fat milk and sugar-free drinks including tea and coffee, and recommends 6 to 8 cups or glasses a day. That is the useful framing: milk counts, and on the measured evidence it counts generously. It is a good choice after a hard session, when you want to keep what you drink. It is a poor choice as the thing you drink all day, and nothing in this data says otherwise.8

  • 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 composition of a drink matters far less than its volume. Follow the number you were given rather than anything derived from a study in healthy young men.

Bar chart titled Milk brings calories that water does not. Calories in a 250 mL glass: whole milk 157 kcal, skim milk 88 kcal, water 0 kcal. Source: USDA FoodData Central.
By USDA's figures, a 250 mL glass of whole milk is about 157 kcal and a glass of skim milk about 88 kcal, against none for water. Swap water for milk to reach a daily fluid target and those calories come with every glass.4 Open full size

Composition

Milk vs water: what is in a glass?

Milk is 88-91% water by weight; what separates it from water is everything else in the glass. Five cow's milks and three plant milks on one scale, with water as the baseline. Switch the serving to the glass you actually drink from.

Serving size

Showing 250 mL · 8.5 fl oz of each.

Composition of five cow's milks, three plant milks and water per 250 mL serving, from USDA FoodData Central
DrinkWaterby weightWater in itper servingCaloriesSugarsProteinSodiumPotassiumCalcium
Whole milk88.1%227mL7.7 fl oz157kcal12.4g8.4g98mg387mg317mg
2% milk89.1%230mL7.8 fl oz129kcal12.6g8.7g101mg410mg325mg
1% milk89.7%231mL7.8 fl oz111kcal12.8g8.7g101mg410mg325mg
Skim milk90.8%234mL7.9 fl oz88kcal13g8.8g106mg431mg340mg
Chocolate milk (1%)84.5%221mL7.5 fl oz168kcal26g9.1g170mg451mg338mg
Oat milk91.3%235mL8 fl oz116kcal5.3g1.7g111mg46mg400mg
Soy milk, unsweetened92.4%238mL8.1 fl oz98kcal1.4g9.2g88mg407mg260mg
Almond milk, unsweetened97.4%251mL8.5 fl oz39kcal0g1.4g155mg80mg446mg
Water (for comparison)99.9%253mL8.6 fl oz0kcal0g0g10mg0mg8mg

USDA publishes composition per 100 grams, so each serving is converted through the item's density — about 1.0313 g/mL for cow's milk. Those densities come from rounded household portion weights, so treat them as good to a couple of percent. Water mass is shown as millilitres on the basis that 1 g of water is 1 mL.4

Which USDA entries these are
  • Whole milk: Milk, whole — FDC 2705385, Food and Nutrient Database for Dietary Studies (FNDDS) 2024-10-31
  • 2% milk: Milk, reduced fat (2%) — FDC 2705386, Food and Nutrient Database for Dietary Studies (FNDDS) 2024-10-31
  • 1% milk: Milk, low fat (1%) — FDC 2705387, Food and Nutrient Database for Dietary Studies (FNDDS) 2024-10-31
  • Skim milk: Milk, fat free (skim) — FDC 2705388, Food and Nutrient Database for Dietary Studies (FNDDS) 2024-10-31
  • Chocolate milk (1%): Chocolate milk, low fat (1%) — FDC 2705470, Food and Nutrient Database for Dietary Studies (FNDDS) 2024-10-31
  • Oat milk: Oat milk — FDC 2705412, Food and Nutrient Database for Dietary Studies (FNDDS) 2024-10-31
  • Soy milk, unsweetened: Soy milk, unsweetened — FDC 2705405, Food and Nutrient Database for Dietary Studies (FNDDS) 2024-10-31
  • Almond milk, unsweetened: Almond milk, unsweetened — FDC 2705409, Food and Nutrient Database for Dietary Studies (FNDDS) 2024-10-31
  • Water (for comparison): Water, tap — FDC 2710707, Food and Nutrient Database for Dietary Studies (FNDDS) 2024-10-31

Your glass

How much water is in a glass of milk?

A 250 mL glass of whole milk carries about 227 mL of water. Pick a milk and a size to see the water in yours, what it costs in calories and sugar, and where it lands against your daily goal.

mL

250 mL · 8.5 fl oz

mL

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

250 mL of whole milk delivers

227mL of water

7.7 fl oz · 88.1% water by weight

Share of your goal11.4%

Counted as volume rather than water content, it is 12.5% 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.9,10

Calories
157kcal
Sugars
12.4g
Protein
8.4g
Sodium
98mg
Potassium
387mg
Calcium
317mg

In Water Goose this logs as Milk at full volume — a 250 mL glass counts as 250 mL, with no hydration multiplier.

Composition from USDA FoodData Central, converted through each drink’s density.4 Work out your daily goal

Questions

More questions about milk and hydration

Does milk hydrate you?

Yes. Milk is about 88-91% water, it counts toward your fluid intake like any other drink, and for a few hours after you drink it your body keeps more of it than it keeps of water. In the trial that created the beverage hydration index, a litre of skim milk scored 1.58 and whole milk 1.50 against water's 1.00, and both left roughly a fifth less urine over the next four hours.1,4,8

Can I drink milk instead of water?

For some of your glasses, yes; for all of them, it is a poor swap. Milk counts toward your fluid intake, and the NHS names lower-fat milk among the drinks that count. Over a few hours it even holds on to fluid better than water. The catch is energy: a 250 mL glass is about 157 kcal of whole milk or 88 kcal of skim, against none for water, and that comes with every glass you swap. Water Goose logs either one at full volume, so the choice is about calories, not about what counts.8,1,4

Can I count milk as water intake?

Yes. The NHS names lower-fat milk among the drinks that count toward fluid intake, EFSA counts water from beverages of all kinds, and NASEM counts the water in drinks and in food toward total intake. Water Goose logs milk as Milk at its full volume, so a 250 mL glass counts as 250 mL. If you want the pedantic version: whole milk is 88.1% water by weight, so that glass carries about 227 mL of actual water.8,9,10,4

Does milk hydrate better than Gatorade?

In the trials that exist, milk kept more fluid than a sports drink, though none tested Gatorade by name: the sports drink was Powerade or an unbranded carbohydrate-electrolyte drink. After exercise in a warm room, people kept 69% of the low-fat milk they drank against 38% of the Powerade. Two more post-exercise trials also put milk ahead, and a fourth found a gap that only approached significance. At rest, both milks scored above water on the hydration index while the sports drink, at 1.02, did not, although that study never compared the drinks with each other. None of these trials gave milk during exercise, and milk carries more calories than a sports drink.3,11,12,13,1

Is milk good for dehydration?

After sweaty exercise, it is one of the better-tested options: in several small trials, people who drank milk after exercise kept more of it than water or a sports drink. Dehydration from vomiting or diarrhoea is a different problem, and none of those trials included anyone who was ill. For that, the NHS advises putting back the lost salts and sugar with an oral rehydration solution a pharmacist can recommend, and lists signs, such as dizziness that does not go away or peeing much less than usual, that need urgent medical advice. Babies, children and older adults are more at risk, so ask a pharmacist or doctor rather than picking a drink from this page.3,11,14

Does milk hydrate you faster than water?

Probably not: milk's advantage is that more of it stays, not that it arrives first. Drinks that carry energy, as milk does, leave the stomach more slowly than water, and the index study's authors give that as one reason less of them turns into urine. The index itself measures how much of a drink you keep over the following hours, not how quickly it reaches your blood, and nothing on this page measured which drink hydrates you fastest.1,15

Is chocolate milk hydrating?

Nobody has run chocolate milk through the beverage hydration index, so there is no measured answer for it. What is known is the composition: USDA's low-fat chocolate milk is 84.5% water against 89.7% for plain 1% milk, and it carries 9.9 g of sugars per 100 g against 4.96 g. It keeps the electrolytes that make plain milk interesting, at 172 mg of potassium and 65 mg of sodium per 100 g, so there is no reason to expect it to hydrate worse. The sugar is real and the evidence is absent.4,1

Is whole milk or skim milk more hydrating?

They performed the same. Skim milk's two-hour index was 1.58 and whole milk's 1.50, both significantly above water, and the authors concluded that fat content did not change the result. Skim is 90.8% water against whole milk's 88.1%, and carries 34 kcal per 100 g against 61. If you are choosing on hydration alone the difference is not measurable; if you are choosing on calories, it is.1,4

Is oat, soy or almond milk hydrating?

They hydrate, but none of them has a beverage hydration index. The closest measurement is a Loughborough trial that matched a soy drink and skim milk for water content and found almost the same urine output over 210 minutes: 950 g after the soy drink against 986 g after the milk. By composition, plant milks are mostly water — USDA puts unsweetened almond milk at 97.4%, unsweetened soy at 92.4% and oat at 91.3%. They are not nutritionally interchangeable with cow's milk, though: almond milk has 0.55 g of protein and 31 mg of potassium per 100 g where whole milk has 3.27 g and 150 mg.7,4

Is milk the most hydrating drink?

Skim milk had the highest mean score of the thirteen drinks tested, but calling it the most hydrating drink oversells one two-hour measurement with about 17 people per drink and a repeatability of roughly 18%. An oral rehydration solution scored 1.54, and the study cannot tell you whether milk beat it: each drink was compared with a pooled water arm, never against the other drinks. The ranking also says nothing about a whole day: the index measures how long a litre stays in you, not whether a drink is a sensible daily habit.1

The rest of the evidence

Is milk better than water after exercise?

In small trials, yes. People who sweated off part of their body weight and then drank back one and a half times the loss kept 69% of low-fat milk against 36% of water and 38% of a sports drink, and stayed in positive fluid balance where the others did not. These are retention percentages in dehydrated people, a different measurement from the index above, so the two never share a scale. The resting trials and the milk-protein studies follow, including the results that did not go milk's way.

  • After exerciseFluid retainedDifferent protocol

    After exercise, people kept 69% of the milk they drank, against 36% of water and 38% of a sports drink (Shirreffs 2007)

    3

    After exercise, milk kept people in net positive fluid balance, whereas water and the sports drink did not.

    Method, results and caveats

    11 adults (5 men, 6 women). Dehydrated by 1.8% of body mass with exercise, then drank 150% of the loss (1.79 ± 0.42 L) over 1 h; 4-h recovery.

    What each group drank in Shirreffs 2007, and what was measured
    WaterreferenceUrine 1205 ± 142 mL; retained 36 ± 10%.
    Carbohydrate-electrolyte sports drinkPoweradeUrine 1184 ± 321 mL; retained 38 ± 16%.
    Low-fat milk (0.2% fat)Urine 611 ± 207 mL; retained 69 ± 10%; net fluid balance +0.01 ± 0.19 L.
    Low-fat milk with added sodium chlorideUrine 550 ± 141 mL; retained 72 ± 4%; net fluid balance +0.06 ± 0.08 L.
    • — Post-exercise, 150% volume: not comparable with BHI values.
    • — People with lactose intolerance were excluded.
  • After exerciseNet fluid balanceDifferent protocol

    Milk drunk at a steady rate after exercise restored fluid balance better overall than water or a sports drink (Seery & Jakeman 2016)

    11

    Overall net fluid balance was higher with milk than with the carbohydrate-electrolyte drink (P=0.001) and water (P=0.006).

    Method, results and caveats

    At the 5-h time point milk beat water (P=0.011), while the comparison with the carbohydrate-electrolyte drink was P=0.077.

    7 men. About 2% body-mass loss from exercise and heat; drank 150% of the loss at a metered rate over 2-3 h.

    What each group drank in Seery & Jakeman 2016, and what was measured
    MilkNet fluid balance at 5 h +117 (SD 122) mL.
    WaterreferenceNet fluid balance at 5 h -539 (SD 390) mL.
    Carbohydrate-electrolyte drinkNet fluid balance at 5 h -381 (SD 460) mL.
    • — Abstract only; n=7.
  • After exerciseFluid retainedDifferent protocol

    Low-fat milk was retained better than water, whether drunk over 30 or 90 minutes (Sayer 2020)

    16

    Low-fat milk was retained more than water at both drinking speeds in the values reported.

    Method, results and caveats

    Not recorded in the evidence file. Drink volume equal to 100% of sweat loss; water or low-fat milk drunk over 30 or 90 min.

    What each group drank in Sayer 2020, and what was measured
    Water over 30 minreferenceRetention 57 ± 16%.
    Water over 90 minreferenceRetention 60 ± 20%.
    Low-fat milk over 30 minRetention 83 ± 6%.
    Low-fat milk over 90 minRetention 85 ± 7%.
    • — Abstract only.
  • After exerciseNet fluid balanceDifferent protocol

    In the heat, milk's edge over a sports drink only approached significance (Watson 2008)

    13

    Milk left people in slightly positive balance; the difference of 326 ± 354 mL only approached significance (P=0.051).

    Method, results and caveats

    Time to exhaustion was the same (39.7 ± 8.1 vs 39.6 ± 7.3 min).

    7 men. 2.0% body-mass loss in a hot, humid environment; drank 150% of the loss; exercise capacity tested afterwards.

    What each group drank in Watson 2008, and what was measured
    Skimmed milkNet fluid balance +191 ± 162 mL; protein intake 75 ± 8 g on the milk trial.
    Carbohydrate-electrolyte drinkNet fluid balance -135 ± 392 mL.
    • — Abstract only; n=7.
    • — Heart rate and rectal temperature were higher on the milk trial.
  • After exerciseFluid retainedDifferent protocol

    Cow's milk, soy milk and a milk-based supplement each kept more fluid than Powerade (Desbrow 2014)

    12

    Each of the other three drinks had higher reported retention than the sports drink.

    Method, results and caveats

    Not recorded in the evidence file. Post-exercise rehydration; abstract only.

    What each group drank in Desbrow 2014, and what was measured
    Sustagen SportRetention 65.1 ± 14.7%.
    Soy milkRetention 46.9 ± 19.9%.
    Cow's milkRetention 40.0 ± 24.9%.
    PoweradeRetention 16.6 ± 16.5%.
    • — Abstract only.
  • At restUrine outputDifferent protocol

    At rest, milk was retained longer in young men but not in older men (Rodriguez-Sanchez 2023)

    5

    Milk improved fluid retention in young men but not in older men, who already retained more water.

    Method, results and caveats

    12 young (24.5 y) and 11 older (63.8 y) men. 1 L over 60 min (250 mL every 15 min); urine for 3 h; no BHI calculated. Macronutrients from labels; electrolytes by flame photometry, with 'mmol' headers that give no volume.

    What each group drank in Rodriguez-Sanchez 2023, and what was measured
    WaterreferenceCumulative urine at 1, 2 and 3 h: young 825, 1082, 1177 g; older 544, 791, 987 g.
    Fruit juice drink (reduced sugar)Tropicana Trop50 (UK)Cumulative urine at 1, 2 and 3 h: young 773, 1009, 1082 g; older 599, 878, 1037 g.
    Sports drinkLucozade Sport (UK)Cumulative urine at 1, 2 and 3 h: young 804, 1034, 1120 g; older 610, 861, 994 g.
    Low-fat (1%) milkCumulative urine at 1, 2 and 3 h: young 635, 822, 956 g; older 625, 851, 978 g. Net fluid balance after milk differed from water in the young men only.
    • — No BHI reported; ratios of group-mean urine are not individual-level BHI, so none are given.
    • — 60-min drinking, men only, small groups.
  • At restUrine outputDifferent protocol

    A soy drink and skim milk, matched for water, gave almost the same urine output (Peden 2024)

    7

    Soya drink and skimmed milk gave similar urine output.

    Method, results and caveats

    10 men. Each drink's volume set to deliver 1000 mL of water; urine over 210 min (30 min of drinking plus 180 min); no water trial.

    What each group drank in Peden 2024, and what was measured
    Skimmed milkSainsbury'sTotal urine 986 ± 254 g.
    Soya drinkAlproTotal urine 950 ± 248 g (P=0.435 vs milk).
    • — No water arm, so no BHI.
  • After exerciseFluid retainedDifferent protocol

    Swapping some carbohydrate for milk protein raised the share of a drink that was kept (James 2013)

    17

    Both carbohydrate-milk protein drinks were retained better than the carbohydrate-only drink (59% and 64% vs 46%, P<0.01); the higher protein dose was no better than the lower one.

    Method, results and caveats

    8 healthy men. Post-exercise rehydration at 150% of body mass lost. All drinks 1087 kJ/L; Na about 20-21 and K 4-5 mmol/L; fat 0.7 g/L; osmolality 280, 264 and 252 mOsm/kg listed in the order C, CP20, CP40.

    What each group drank in James 2013, and what was measured
    CRetention 46 ± 9%; net fluid balance -470 ± 154 mL.
    CP20Retention 59 ± 12%; net fluid balance -181 ± 280 mL.
    CP40Retention 64 ± 6%; net fluid balance -107 ± 126 mL.
    • — Post-exercise protocol.
  • After exerciseFluid retainedDifferent protocol

    Whey protein on its own kept no more fluid than water (James 2014)

    18

    Whey protein isolate alone did not improve retention over water.

    Method, results and caveats

    Not recorded in the evidence file. Post-exercise rehydration; abstract only.

    What each group drank in James 2014, and what was measured
    WaterreferenceUrine 1234 ± 358 mL; retention 40 ± 14%.
    Whey protein isolateUrine 1306 ± 268 mL; retention 37 ± 14%.
    • — Abstract only.

Mechanism

Why does milk hydrate you better than water?

Nothing exotic. Milk carries energy, which slows how fast it leaves the stomach, and sodium and potassium, which help the body keep the water it absorbs; after exercise, its protein seems to add something of its own. Here is the evidence behind each, and how strong it is.

  • Moderate evidenceOther

    The index study's authors give two reasons for milk's score. Drinks that carry energy, whether as carbohydrate, fat, protein or alcohol, leave the stomach more slowly than energy-free drinks, which can reduce or delay the urine that follows; and the drinks richest in sodium and potassium, the oral rehydration solution and both milks, tended to have the highest index.1

    Energy density: full-fat milk 640 kcal/L, orange juice 470, cola 420, skimmed milk 350, lager 330. High energy was generally associated with a high index, but cola, lager and orange juice show that other factors matter too.

    Caveat: The authors' explanation rather than a measurement: the trial did not measure gastric emptying.

  • Moderate evidenceRandomised trial

    The beverage hydration index study attributes milk's high score to its electrolytes and energy. Full-fat and skimmed milk scored alike, so fat content did not change the result.1

    2-h BHI: full-fat milk 1.50 ± 0.58 (3.6 g fat/100 mL, 640 kcal/L); skimmed milk 1.58 ± 0.60 (0.1 g fat/100 mL, 350 kcal/L). Corrected effect sizes 0.89 and 1.14. Both milks Na 18-19 and K 40-41 mmol/L.

    Caveat: A single 1 L bolus at rest. Milk's energy load of 350-640 kcal/L matters for everyday use.

  • Moderate evidenceRandomised trial

    At rest and already hydrated, drinks with 27 or 52 mmol/L of sodium produced less urine and better net fluid balance than drinks with 7 or 15 mmol/L.19

    27 and 52 mmol/L vs 7 and 15 mmol/L sodium (p<.05); 1 L drinks; 4 h.

    Caveat: Abstract only.

  • Moderate evidenceReview

    Large volumes of plain water trigger prompt urination after exercise. Added sodium helps the body keep fluid by maintaining extracellular fluid osmolality and volume, and carbohydrate and protein change how water is absorbed and distributed.2

  • Moderate evidenceReview

    Skimmed milk rehydrates better than a carbohydrate-electrolyte sports drink after exercise, and part of the effect seems to come from milk protein, which beat an equal-energy amount of carbohydrate. Evidence for whey protein is mixed.20

    Caveat: Abstract only.

  • Moderate evidenceReview

    A rehydration drink's volume must exceed the water lost, and its formulation controls how fast it leaves the stomach and is absorbed in the small intestine.15

    Caveat: Abstract only; a corrigendum exists.

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
Cow's milk, pasteurised6277.8mOsm/kgSD 820
Cow's milk, UHT6282.7mOsm/kgSD 7.95
Cow's milk, skim, UHT6273mOsm/kgSD 7.710
Cow's milk, lactose-reduced, UHT6Splitting lactose into glucose and galactose raises osmolality.389.1mOsm/kgSD 5.65
Soy-based drink6213.7mOsm/kgSD 8.410
Milk permeate oral hydration solution224% carbohydrate, Na 21, K 28 mmol/LHyperosmolal, yet it retained more fluid than water in the same study.621mOsm/kgSD 5—

Labels

What the milk and plant-milk labels say

Published panels for products people actually buy. These are label values for one flavour and package, 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
fairlife232% Reduced Fat Ultra-Filtered Milk1 cup (240 mL)1206 g13 g120 mg400 mg
Oatly24Original Oatmilk1 cup (240 mL)1207 g3 g100 mg390 mg
Silk25Original Almondmilk1 cup (240 mL)607 g1 g150 mg0 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.

  • fairlife 2% Reduced Fat Ultra-Filtered Milk: Total fat 4.5 g; calcium 380 mg. Contains lactase enzyme.
  • Oatly Original Oatmilk: 7 g added sugars; total fat 5 g; fibre 2 g; calcium 350 mg.
  • Silk Original Almondmilk: Potassium is printed on the panel as 0 mg.
  • Silk Original Almondmilk: 7 g added sugars; total fat 2.5 g; calcium 470 mg.

Receipts

Where the milk numbers come 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
  • — 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.
  • — Berry 2020: Funded by Dairy Management Inc.

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

    Evans GH, James LJ, Shirreffs SM, Maughan RJ. Optimizing the restoration and maintenance of fluid balance after exercise-induced dehydration. J Appl Physiol 2017;122(4):945-951.

    StudyRead: abstractOpen source

  3. 3

    Shirreffs SM, Watson P, Maughan RJ. Milk as an effective post-exercise rehydration drink. Br J Nutr 2007;98(1):173-180.

    StudyRead: full textOpen source

    The paper calls the milk 'low-fat milk (0.2% fat)'. Its abstract lists the water and sports-drink urine volumes in reverse order; evidence.ts uses the Results.

  4. 4

    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.

  5. 5

    Rodriguez-Sanchez N, Galloway SDR. A randomised trial to assess fluid and electrolyte balance responses following ingestion of different beverages in young and older men. Eur J Appl Physiol 2023;123(10):2331-2340.

    StudyRead: full textOpen source

    Same urine protocol as the BHI, but drinks taken over 60 min and no BHI calculated.

  6. 6

    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).

  7. 7

    Peden DL, et al. (senior author James LJ). Eur J Appl Physiol 2024.

    StudyRead: full textOpen source

    Loughborough University. Skimmed milk vs soya drink fluid retention; no water arm. Data on figshare (26075815).

  8. 8

    NHS. Water, drinks and hydration. Page last reviewed 17 May 2023.

    GuidelineRead: official pageOpen source

    Next review was due 17 May 2026, so the review is overdue as of September 2026.

  9. 9

    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.

  10. 10

    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.

  11. 11

    Seery S, Jakeman P. A metered intake of milk following exercise and thermal dehydration restores whole-body net fluid balance better than a carbohydrate-electrolyte solution or water in healthy young men. Br J Nutr 2016;116(6):1013-1021.

    StudyRead: abstractOpen source

  12. 12

    Desbrow B, et al. Appl Physiol Nutr Metab 2014.

    StudyRead: abstractOpen source

  13. 13

    Watson P, Love TD, Maughan RJ, Shirreffs SM. A comparison of the effects of milk and a carbohydrate-electrolyte drink on the restoration of fluid balance and exercise capacity in a hot, humid environment. Eur J Appl Physiol 2008;104(4):633-642.

    StudyRead: abstractOpen source

  14. 14

    NHS. Dehydration. Health A to Z. Page last reviewed 1 May 2026.

    GuidelineRead: official pageOpen source

    Read 2026-09-25. Says that if you are being sick or have diarrhoea you need to replace the sugar, salts and minerals lost, and that a pharmacist can recommend oral rehydration solutions; babies, children and older adults are more at risk. Its line that caffeinated drinks dehydrate you is not used here: it conflicts with the caffeine evidence on the soda page.

  15. 15

    Leiper JB. Fate of ingested fluids: factors affecting gastric emptying and intestinal absorption of beverages in humans. Nutr Rev 2015;73(Suppl 2):57-72.

    StudyRead: abstractOpen source

    Corrigendum: Nutr Rev 2020;78(9):781 (PMID 32159769).

  16. 16

    Sayer L, et al. Int J Sport Nutr Exerc Metab 2020.

    StudyRead: abstractOpen source

  17. 17

    James LJ, et al. Br J Nutr 2013;110:1285-1291.

    StudyRead: full textOpen source

  18. 18

    James LJ, et al. Amino Acids 2014.

    StudyRead: abstractOpen source

  19. 19

    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).

  20. 20

    James L. Milk protein and the restoration of fluid balance after exercise. Med Sport Sci 2012;59:120-126.

    StudyRead: abstractOpen source

  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

    Berry CW, Wolf ST, Murray B, Kenney WL. Hydration efficacy of a milk permeate-based oral hydration solution. Nutrients 2020;12(5):1502.

    StudyRead: full textOpen source

    Funding: Funded by Dairy Management Inc.

  23. 23

    fairlife. 2% Reduced Fat Ultra-Filtered Milk, nutritional facts.

    Product labelRead: official pageOpen source

  24. 24

    Oatly US. Original Oatmilk 32 oz, nutrition facts.

    Product labelRead: official pageOpen source

  25. 25

    Silk. Original Almondmilk, nutrition facts.

    Product labelRead: official pageOpen source

How the study numbers were read

Maughan 2016: 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 abstract says the BHI was corrected for water content, but the 1.58, 1.54 and 1.50 values are the uncorrected BHI. The lager's alcohol content was not reported, and no numeric 4-h BHI was reported for any drink. Shirreffs 2007: The abstract lists the water and sports-drink urine volumes in reverse order; the Results values are used here. Peden 2024: Urine by time point is shown only in a figure and is not used.1,3,7

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

This page can tell you that a 250 mL glass of milk carries about 227 mL of water. Water Goose is what remembers you drank it.

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