Heatwave hydration

Hot days need more than your usual mugs. A simple daily drinks target, plus the signs that mean you need to cool down now.

Your details

Sex
Hours active outside
Sweat rate

Gentle walking in the heat might be 0.3 to 0.5 litres an hour; hard work or sport can be much more. The sweat loss calculator can measure yours.

A hot day with 2.0 hours active outside

2.6 litres

of drinks through the day

  • Everyday drinks (EFSA)1.6 litres
  • Extra for sweat (0.5 litres an hour)1.0 litres
  • In 250 ml glasses11
  • In pints4.6

Sip regularly rather than drinking a lot at once, and go for cool water or squash: the NHS suggests avoiding alcohol, caffeine and hot drinks in a heatwave. Pale straw coloured pee is a good sign. Sweat rates vary a lot from person to person, so adjust the box to suit you. If you have heart or kidney problems or have been told to limit fluids, follow your own team's advice.

Heat exhaustion (headache, dizziness, feeling sick, heavy sweating) should improve within 30 minutes of cooling down and drinking. Call 999 if someone is still unwell after 30 minutes of resting somewhere cool and drinking, has hot skin that is not sweating, is confused, breathing fast, has a fit or loses consciousness.

The working

A woman active for 2 hours in the heat

EFSA puts a woman's everyday water from drinks at about 1.6 litres (80% of 2.0 litres). Two hours at 0.5 litres an hour adds 1 litre, so the target is about 2.6 litres, roughly 11 glasses of 250 ml or 4.6 pints, sipped through the day.

Keeping cool

NHS heatwave advice

  • Stay in the shade, especially between 11am and 3pm
  • Have regular cold drinks, and avoid alcohol, caffeine and hot drinks
  • Avoid exercise or activity that makes you hotter
  • Close curtains in the day and open windows at night when it is cooler outside
  • Check on anyone at higher risk, such as older people, babies and people with long term conditions

Heat exhaustion

Spot it early

Signs include cramps, a high temperature, feeling very thirsty and irritable. Move to a cool place, take off extra layers, drink water or a rehydration drink and cool the skin. They should feel better within 30 minutes. Call 999 if they are still unwell after 30 minutes of this, or have hot skin that is not sweating, fast breathing, confusion, a fit or lose consciousness.

Read with care

What this cannot tell you

  • Know your sweat rateIt varies with fitness, effort, clothing and humidity.
  • Replace medical adviceSome heart and kidney conditions need a fluid limit; follow your care team.
  • Cool you downShade, rest and cool water on the skin matter as much as drinking.

Questions

Common questions

How much water should I drink in a heatwave?

More than usual. Start with about 1.6 litres of drinks for women or 2.0 for men, then add what you sweat when active.

Is tea OK in hot weather?

Everyday tea counts as fluid, but in a heatwave the NHS suggests cold drinks and avoiding caffeine, alcohol and hot drinks.

Should I sip or gulp?

Sip regularly through the day. The NHS heatwave advice is regular cold drinks rather than waiting until you are very thirsty.

When is heat an emergency?

Call 999 for signs of heatstroke, such as hot skin that is not sweating, confusion, a fit or losing consciousness, or anyone still unwell after 30 minutes of cooling.

Sources

Last checked 21 October 2026. Spotted something wrong? Tell us and we will fix it.

If heat is making you unwell

Get help from NHS 111 if you are struggling to treat heat exhaustion. Call 999 for signs of heatstroke or if someone is still unwell after 30 minutes of cooling. If you have a heart or kidney condition, ask your GP how much to drink in hot weather.

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