You're three drinks in, your mouth is dry, and someone at the table has already told you to have a glass of water between each round. So: does alcohol dehydrate you, and does the water trick do what people think? The short answer is that yes, alcohol increases fluid loss — but the effect is smaller, shorter and far more dependent on what's in your glass than most people assume. And the research on drinking water alongside alcohol does not support the main thing people use it for. Here's what the published evidence actually says, and what you can do with it tonight.
Does alcohol dehydrate you? What the studies actually measured
Ethanol is a diuretic, and the mechanism has been described since M. G. Eggleton's 1942 paper “The diuretic action of alcohol in man” in the Journal of Physiology. It runs through a hormone called vasopressin, also known as antidiuretic hormone. Vasopressin tells your kidneys to reabsorb water instead of sending it to your bladder; ethanol suppresses it. Less vasopressin, less reabsorption, more urine. That's the whole alcohol vasopressin diuresis chain in one sentence.
What's more interesting is the shape of the effect over time. In their 2024 review in Alcohol, Mackus and colleagues note that Eggleton's own data showed the spike in urine flow was confined to the first two hours after drinking began, and that continuing to drink over the following four hours did not produce a second spike. The diuresis front-loads, then fades.
A 2020 study in the American Journal of Physiology–Renal Physiology complicates the picture further. Sailer and colleagues at University Hospital Basel put ten healthy men through four interventions in random order — beer alone, beer plus water, beer plus salted stock, or water alone — drinking to a blood alcohol concentration of 0.8‰. They measured copeptin, a stable stand-in for vasopressin. At 90 minutes there was no difference in copeptin between the alcohol and water conditions (P = 0.4), even though total urine output was higher in every alcohol condition (P = 0.01). By 720 minutes, copeptin, plasma sodium and urine osmolality were all significantly higher after alcohol than after water alone (P = 0.02) — the body counter-regulating and pulling water back. The authors open their abstract by stating flatly that the effect of alcohol on vasopressin levels “is controversial.”
Drink strength matters more than drink count
The most usable finding comes from a diet-controlled randomised crossover trial published in Nutrients in 2017. Polhuis and colleagues gave 19 Dutch men (median age 69, range 65–75) six beverages on separate days: beer at 5% ABV, wine at 13.5%, spirits at 35%, and their non-alcoholic counterparts. Every alcoholic serve delivered the same 30 g of alcohol — so roughly 600 mL of beer, 222 mL of wine, or 86 mL of spirits.
Wine and spirits produced more urine over four hours than their non-alcoholic counterparts (p < 0.003 and p < 0.001). Beer did not differ from non-alcoholic beer at any time point (p > 0.70). And by the 24-hour collection, none of the differences held (p > 0.40 and p > 0.10). The authors' conclusion: only stronger beverages produced “a short and small diuretic effect.” Same alcohol dose, different outcome — the variable was concentration, and the fluid that came with it.
If you're already dehydrated, the effect shrinks
In Alcohol and Alcoholism, Hobson and Maughan dehydrated 12 men by about 1.9% of body mass through exercise in the heat, then gave them a litre of either 4% beer or alcohol-free beer the next morning. In the well-hydrated men, alcohol raised four-hour urine output to 1279 ± 256 mL versus 1121 ± 148 mL (P < 0.001). In the dehydrated men, the difference was 261 ± 138 mL versus 174 ± 61 mL — and it did not reach significance (P = 0.057). Their conclusion: “the diuretic action of alcohol is blunted when the body is hypohydrated.” Your kidneys defend fluid volume even against ethanol. That is not protection — it means you were already in deficit.
Hydration and drinking: does a glass of water between rounds work?
This is where the popular story falls apart. The Mackus review searched for every human study on hangover and water and found only 13. Among them: a survey of 462 Dutch students in which water was the most popular hangover remedy, used by 55.8% of them, with a mean self-rated efficacy of 5.8 on a 0–10 scale — modest. A second survey of 826 students rated water during drinking at 5.2 (SD 2.4, n = 618) and water before bed at 5.6 (SD 2.6, n = 502).
The most telling data came from 307 people walking the 15.8 km Samaria Gorge in Crete, 176 of whom were hung over. They drank a mean of 2.7 L of water during the walk. Water consumed correlated positively with hangover severity (r = 0.176, p = 0.019 before the walk; r = 0.243, p < 0.001 during) — worse hangovers make you drink more, not the reverse. But water intake showed no significant relationship to the change in hangover severity (r = 0.103, p = 0.174; r = 0.066, p = 0.388). Drinking more water tracked with feeling worse; it did not track with getting better. A separate placebo-controlled trial in 214 participants found no evidence of significant dehydration during the hangover state at all.
The review's conclusion is that hangover and dehydration are “two co-occurring but independent consequences of alcohol consumption.” Water is genuinely good at fixing thirst and dry mouth. It is not, on this evidence, what fixes a headache.
What the research does not show
- It does not show that any drink is hydrating. Nothing here says a lower-strength drink adds net water. It says the diuretic signal is smaller and shorter.
- The samples are small and male. Twelve men, 19 elderly men, ten men. Polhuis and colleagues state explicitly that applicability to women is uncertain, since body composition differs and hormonal effects on fluid balance cannot be excluded.
- Much of it is old and underpowered. Mackus and colleagues note most of the experimental studies they found were conducted more than 40 years ago with small samples, and the surveys rely on retrospective self-report.
- There is a hole in the literature. The same review states there are no experimental studies specifically testing whether water intake counteracts dehydration and hangover. That is absence of evidence, not proof water is useless.
- Conditions were artificial. Hobson and Maughan induced dehydration by exercising people in the heat; Polhuis's 24-hour collections were unsupervised at home.
What to actually do
- Rehydrate before you drink, not just during. If you've come off a hot patio day, a run or a sauna, the fluid deficit is already there. Fix it with water first.
- Front-load your caution, not your drinks. The diuretic response clusters in the first couple of hours. Pace the start of the evening.
- Think in grams of alcohol, not glasses. One 30 g dose was a bottle of beer, a large glass of wine, or a shot. Concentration is what changed the result.
- Drink water for thirst — and be realistic. It will help the dry mouth. Expect a modest effect on tomorrow, not a rescue.
- Know the Canadian benchmarks. Canada's Guidance on Alcohol and Health (CCSA, 2023) places 1–2 drinks a week at low risk, 3–6 at moderate risk, and 7 or more at increasingly high risk, with no more than 2 on any one day.
Where hydrating cocktails actually fit
“Hydrating cocktails” is a search term, not a category the research recognises. No cocktail hydrates you the way a glass of water does. What genuinely varies between drinks is how much alcohol arrives per serve and how much fluid it arrives with — the same variable that separated beer from spirits in the Polhuis trial.
That's the design brief behind our vodka water cocktails. Aura is premium distilled vodka and alkaline water (pH 8.5+) with natural flavour, in a 355 mL can — a long, dilute serve rather than a concentrated one. It's still, with zero carbonation, so there are no bubbles and no bloating. No added sugar, no artificial sweeteners, no preservatives, and gluten-free, in Cucumber Lime, Coconut Pineapple and Mango Peach. To be clear about what that is and isn't: the alcohol in the can is the same alcohol, and none of the research above makes Aura healthier, safer or less intoxicating than anything else. It's a cleaner-tasting format, not a health product. More on the thinking behind it on why Aura.
Aura is available across British Columbia, Alberta and Ontario. Our own direct and wholesale ordering delivers to Ontario addresses only. In Alberta, look for Aura at AGLC-licensed private retailers; in B.C., at BC Liquor Stores and licensed private retailers — check where to buy for the closest stockist.
Planning a long summer afternoon in Canada? Start hydrated, keep water on the table for what water is actually good at, and pick a drink you're happy to sip slowly. If that sounds like your kind of evening, browse our vodka water cocktails and order a case of 24 to your Ontario address, or find Aura near you at where to buy. Please enjoy responsibly, and only if you are of legal drinking age in your province.
This article summarises published research for general interest and is not medical advice.
Sources
- Eggleton MG. The diuretic action of alcohol in man. Journal of Physiology. 1942;101(2):172–191. doi:10.1113/jphysiol.1942.sp003973. PMID 16991552. PubMed record (findings cited here as summarised by Mackus et al., 2024).
- Hobson RM, Maughan RJ. Hydration status and the diuretic action of a small dose of alcohol. Alcohol and Alcoholism. 2010;45(4):366–373. doi:10.1093/alcalc/agq029. PMID 20497950. PubMed
- Polhuis KCMM, Wijnen AHC, Sierksma A, Calame W, Tieland M. The diuretic action of weak and strong alcoholic beverages in elderly men: a randomized diet-controlled crossover trial. Nutrients. 2017;9(7):660. doi:10.3390/nu9070660. PMID 28657601. PubMed
- Sailer CO, Refardt J, Bissig S, Bologna K, Imber C, Christ-Crain M. Effects of alcohol consumption on copeptin levels and sodium-water homeostasis. American Journal of Physiology–Renal Physiology. 2020;318(3):F702–F709. doi:10.1152/ajprenal.00458.2019. PMID 31961713. PubMed
- Mackus M, Stock A-K, Garssen J, Scholey A, Verster JC. Alcohol hangover versus dehydration revisited: the effect of drinking water to prevent or alleviate the alcohol hangover. Alcohol. 2024;121:9–18. doi:10.1016/j.alcohol.2024.07.006. PMID 39069212. PubMed
- Canadian Centre on Substance Use and Addiction. Canada's Guidance on Alcohol and Health. Ottawa: CCSA, 2023. ccsa.ca