Sauna Dehydration: How to Stay Hydrated UK 2026

Sweat rates vary with the heat, the length of the session and the person, but it is common to lose somewhere around half a litre to a litre of fluid in a typical sauna visit, and more over a long or repeated session. That is why dehydration is a real risk and the post-sauna thirst is real and worth answering. The goal is not to drink enormous amounts during the session, but to start hydrated and to replace what you lose across the hours afterwards. For more on session length, see our guide to how long to sauna for benefits.

Before: a glass or two of water in the half hour beforehand sets you up well. During: if you do several rounds, sip water in the cool-down breaks rather than forcing large amounts in one go. After: keep drinking steadily for the next hour or two until your thirst settles and your urine runs pale. Plain water is enough for most sessions. Avoid relying on alcohol or sugary drinks to rehydrate, and skip caffeine in large amounts straight after, as it offers no advantage here.

For a normal session, water is fine and your next meal replaces the small amount of salt lost in sweat. Electrolytes, sodium, potassium and magnesium, become worth considering only if you sauna for a long time, do several sessions back to back, or sauna daily on top of heavy exercise, when sweat losses add up. In those cases an electrolyte drink or a pinch of salt with water helps you rehydrate more effectively than water alone. Most casual users do not need them.

Watch for a headache, dizziness or light-headedness, a dry mouth, dark urine, cramps, or feeling unusually tired or weak after a session. If any appear, stop, cool down, and drink water steadily. Persistent or severe symptoms, such as fainting, confusion or a racing heart, need prompt medical attention. Our guide to who should not use a sauna covers the people and conditions that need extra caution with heat. This article is general guidance, not medical advice.

Some people lose fluid faster or feel the effects sooner, and it is worth knowing if that includes you. Older adults are more vulnerable because the sense of thirst weakens with age, so the usual signal to drink is less reliable. Anyone taking diuretics or certain blood-pressure medications is also more prone to dehydration, since those drugs increase fluid loss in the first place; if that is you, it is worth a word with your GP before regular hot sauna use.

Alcohol is the other big one. Drinking before or during a sauna is a genuinely bad idea: it dehydrates you further, impairs your judgement about when to leave, and adds strain to the heart in the heat. Pregnancy and underlying heart conditions are reasons to be cautious too, keeping sessions short, cool and well-hydrated, and to take medical advice first.

Yes, and for longer sessions it is a good idea. Sipping water while you are in the heat helps you keep pace with what you are sweating out, rather than arriving at the end already well behind. Take in a suitable bottle and drink little and often rather than gulping a lot at once.

Just be sensible about the container: never take glass into a hot sauna, where it can crack or shatter, and avoid single-use plastics that are not meant for heat. A sturdy stainless steel or heat-safe bottle is ideal. If you would rather not drink inside, step out between rounds for a drink instead, which also gives your body a natural cool-down break.