How much water should I drink on a long-haul flight?

Rather than a fixed number, drink steadily and use pale-yellow urine as your guide. Many travellers find about a litre across a long flight works, and an aisle seat makes it practical.

Do I need electrolyte drinks on a flight?

Most healthy travellers do not. Their main benefit is making water more appealing so you drink more of it. If you take diuretics or have blood pressure, kidney, or heart conditions, check the sodium content with your doctor first.

Does alcohol dehydrate you more at altitude?

Alcohol increases fluid loss and worsens sleep quality, and the very dry cabin air already adds to dehydration. Health guidance for long flights generally recommends limiting it.

Hydration

Hydration on long flights

Cabin humidity is very low, so you lose fluid steadily through breathing and skin. Drinking to pale-yellow urine, limiting alcohol, and planning an aisle seat solves most of the arrival headache.

5 min read. Last updated 2026-06-20.

Why flights dry you out

Cruising cabin air is far drier than almost any environment on the ground. You lose water constantly through breathing and your skin, and because you are not hot, you do not feel thirsty in proportion to the loss.

A workable plan

Judge by output, not by a fixed target, and set yourself up so drinking is not inconvenient.

Fill a 1-litre bottle after security; aim to finish it across a long flight
Aim for pale-yellow urine rather than a set number of glasses
Book an aisle seat if you will be drinking properly
Limit alcohol; it worsens sleep quality and adds to fluid loss
Coffee and tea count toward fluid, but keep them to destination-morning hours
Lip balm, a saline nasal spray, and eye drops handle the dryness you feel most

When to be careful

If you take diuretics or have heart, kidney, or liver conditions, your fluid and salt targets may be specific to you. Ask your doctor rather than following a general guideline.

Electrolytes: useful or hype?

For most healthy travellers, water is enough. Electrolyte sachets are mostly useful because they make water more pleasant to drink, and in hot destinations with a lot of walking. Check the sodium content if you have high blood pressure.

Things worth buying properly

Electrolyte drink packets

Budget · $1–$2 per serving

Makes plain water easier to actually drink on a dry flight.

What to look for

Contoured blackout sleep mask

Budget · $15–$30

Darkness is the cheapest sleep aid you can carry.