You've probably heard you should drink a glass of water for every hour in the air. It's a neat rule, but it isn't based on research. Here's what we actually know about hydration when you fly, and why your gut cares.
Written by Vita Globe Editorial Team | Reviewed against CDC travel guidance and National Academies nutrient recommendations
How much water should you drink on a plane?
There's no official in-flight target. Your baseline needs don't change much: the National Academies set adequate total water intakes of about 3.7 liters a day for men and 2.7 liters for women, including water from food[1]. Cabin air is very dry, typically 10% to 20% humidity[2], so the practical advice is to sip regularly, go easy on alcohol[3] and not skip drinks to avoid the bathroom.
Caveat: Popular "one glass per hour" rules aren't backed by studies, and the CDC describes the effects of dry cabin air mainly in terms of dry eyes and airways.
Sources: IOM water DRIs · CDC Yellow Book: air travel · CDC Yellow Book: jet lag · Verified 2026-09-28
In this article
Does flying actually dehydrate you?
Cabin air is dry. The CDC describes it as typically 10% to 20% humidity, which can dry out your eyes and upper airway[2]. That dryness is what makes your throat feel scratchy and your contacts uncomfortable.
Whether a normal flight causes meaningful dehydration is less clear. The bigger issue for most people is behavior: skipping drinks to avoid climbing over a seatmate, filling up on coffee and wine, and a travel day that started at 4 a.m. without breakfast.
So how much should you drink?
Start with your normal needs. The National Academies' adequate intakes are about 3.7 liters of total water a day for men and 2.7 liters for women, and that includes water from food as well as drinks[1]. Most healthy people meet their needs by drinking with meals and when thirsty.
On a flight, that translates into a few simple habits:
- Bring an empty refillable bottle through security and fill it at the gate.
- Take water every time the drink cart comes by, even if you also order something else.
- Sip steadily rather than downing a big bottle right before boarding.
- If you're traveling somewhere with uncertain tap water, switch to factory-sealed bottled water once you land[7].
Should you skip alcohol and coffee on a flight?
You don't have to skip them, but it helps to keep them in check. The CDC's jet lag guidance recommends avoiding excess alcohol because it worsens sleep and contributes to dehydration[3]. The same guidance allows caffeine during daylight hours but suggests stopping several hours before bed at your destination[3]. A simple pattern: one drink, then water.
Why does hydration matter for your gut on a trip?
Not drinking enough is a recognized cause of constipation[4]. A review on hydration and constipation found that extra water helps mainly when you're under-hydrated, and doesn't add much for people already drinking enough[5]. Travel days are exactly when many of us fall below our usual intake, so keeping up is one of the easiest ways to avoid getting backed up.
The trips to the bathroom have a side benefit too. The CDC recommends moving around every one to two hours on trips longer than four hours to reduce blood clot risk[6]. For more on flight-day comfort, see Why You Get Bloated on a Plane.
The honest summary
- There's no proven in-flight water target; aim to meet your normal daily needs.
- Cabin air is very dry, so sip regularly and don't skip drinks to avoid the bathroom.
- Keep alcohol modest; it worsens sleep and adds to dehydration.
- Staying hydrated is one of the easiest ways to avoid travel constipation.
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Frequently asked questions
Is one glass of water per hour of flying a good rule?
It's an easy reminder, but it isn't based on research. Meeting your normal daily needs and sipping regularly is a sensible goal[1].
Why is airplane air so dry?
Cabin humidity is typically only 10% to 20%, which dries the eyes and airways[2].
Does alcohol dehydrate you more on a plane?
Alcohol contributes to dehydration and worsens sleep, so the CDC advises avoiding excess on long trips[3].
Can not drinking enough on a flight cause constipation?
It can contribute. Dehydration is a recognized cause of constipation[4], and extra fluid helps most when you're under-hydrated[5].
Should I drink tap water when I land abroad?
Only where it's known to be safe. Otherwise, choose factory-sealed bottled water or drinks made with boiled water[7].
Sources
- Institute of Medicine. Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate. Washington, DC: The National Academies Press; 2005. doi:10.17226/10925
- Mase SR, Gearhart SL, Nardell EA, Brown CM. Air travel. In: CDC Yellow Book 2026: Health Information for International Travel. Centers for Disease Control and Prevention. cdc.gov
- Riedy SM, Williams SG. Jet lag disorder. In: CDC Yellow Book 2026: Health Information for International Travel. Centers for Disease Control and Prevention. cdc.gov
- National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). Symptoms & Causes of Constipation. National Institutes of Health. niddk.nih.gov
- Arnaud MJ. Mild dehydration: a risk factor of constipation? Eur J Clin Nutr. 2003;57(Suppl 2):S88-S95. doi:10.1038/sj.ejcn.1601907
- Centers for Disease Control and Prevention. Understanding your risk for blood clots with travel. cdc.gov
- Chard AN, Hill V. Food and water precautions for travelers. In: CDC Yellow Book 2026: Health Information for International Travel. Centers for Disease Control and Prevention. cdc.gov
About the Vita Globe Editorial Team
The Vita Globe Editorial Team researches and writes our wellness content, working from peer-reviewed research, systematic reviews and guidance from bodies such as the NIH and the FDA. We cite our sources inline and update articles when the evidence changes.
These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease. This article is for informational purposes only and is not a substitute for medical advice. Talk to your healthcare provider before starting any new supplement, particularly if you are pregnant, nursing, taking medication, or caring for a child.
