How to Stay Hydrated in Hot Weather
To stay hydrated in hot weather, carry water with you, drink regularly through the day without waiting until you feel thirsty, and check that your pee stays light yellow or clear. The World Health Organization suggests about one cup of water an hour and at least 2–3 liters (about 68–101 fl oz) a day during heat. If you work or exercise in the heat, plan your drinks; for workers, US guidance generally caps fluid at 6 cups (about 1.4 liters) an hour.
How much to drink in hot weather
The US National Academies put it plainly: "Higher intakes of total water will be required for those who are physically active or who are exposed to hot environments." There's no single number that fits everyone, but the main health agencies agree on the approach.
- Don't wait for thirst. The CDC's advice for extreme heat is to "drink more water than usual" and "don't wait until you're thirsty."
- Keep water with you. "Carry a water bottle. Drink and refill it throughout the day," says the CDC.
- Use a rough hourly guide. The WHO suggests drinking water regularly: about 1 cup an hour and at least 2–3 liters (about 68–101 fl oz) a day. The WHO doesn't say how big the cup is, so treat this as a rough guide, not a target to hit exactly.
- Reach for cold drinks. The NHS suggests drinking more cold drinks, especially if you're active or exercising.
- Go easy on some drinks. The CDC suggests cutting back on drinks high in sugar and sodium, as well as caffeine and alcohol.
- Check your pee. "When it's light yellow or clear, it usually means you are drinking enough water," says the CDC. For what darker pee and other symptoms can mean, see signs of dehydration.
Long hot days make it easy to forget to drink. If that sounds like you, set reminders on your phone or watch. A water tracker such as Hydrolotl can send them, with quiet hours for the night.
Working or exercising in the heat
For people who work in the heat, the CDC's National Institute for Occupational Safety and Health (NIOSH) gives specific numbers:
| Situation | NIOSH guidance |
|---|---|
| Moderate activity in the heat lasting under 2 hours | 1 cup, 237 ml (8 fl oz), of water every 15–20 minutes |
| Upper limit | Generally no more than 6 cups an hour, about 1.4 liters (48 fl oz) |
| Sweating for several hours | Sports drinks containing balanced electrolytes |
| Drinks to avoid | Alcohol, and drinks with high caffeine or sugar |
The CDC also counts people exercising outdoors among those who need extra care in the heat. If you train in warm weather, our guide to water during exercise covers weighing yourself before and after a session and building a plan that fits your own sweat losses.
Don't overdo it
Notice that NIOSH sets a ceiling as well as a target. Drinking large amounts of fluid much faster than your kidneys can clear it has caused acute water intoxication, according to the National Academies. Too much water too fast can lower the sodium in your blood, a condition called hyponatremia, so "more is better" isn't true for water. Read more in can you drink too much water.
If a doctor has told you to limit fluids (for example for heart failure or kidney disease), follow their limit rather than general advice, and ask them how to handle hot spells.
Who needs extra care in the heat
The CDC names these groups as needing extra care when it's hot:
- infants and young children
- people aged 65 and older
- people with heart disease
- people with asthma, especially children
- pregnant women
- outdoor workers and people exercising outside
The WHO adds people with lung or kidney conditions, people with a disability, and people living alone. Older adults have a particular reason not to rely on thirst: the National Academies note that "thirst and fluid intake are impaired in the elderly." If you have an older relative or neighbor, a check-in on a hot day, with a drink offered, is a kind and practical thing to do.
Heat exhaustion vs heatstroke
Heat can make people ill in two main ways, and the difference matters. Heat exhaustion can usually be handled with first aid: the NHS says a person should start to cool down and feel better within 30 minutes. Heatstroke is different: the WHO calls it a medical emergency.
| Heat exhaustion | Heatstroke | |
|---|---|---|
| Typical signs | Tiredness, dizziness, headache, nausea or vomiting, cramps, strong thirst, heavy sweating, pale and clammy skin, high temperature | Very high temperature, hot skin that isn't sweating, fast heartbeat or fast breathing, confusion or lack of coordination, a seizure or loss of consciousness |
| How serious | Should start to improve within 30 minutes of first aid | A medical emergency |
| What to do | Move to a cool place, give water or a sports or rehydration drink, cool the skin | Call your local emergency number straight away |
When to call for emergency help
The NHS says to call 999, the UK emergency number, if someone in the heat:
- is still unwell after 30 minutes
- has a very high temperature, or hot skin that isn't sweating
- has a fast heartbeat or fast breathing
- is confused or has lost their coordination
- has a seizure or loses consciousness
Wherever you are, call your local emergency number and follow the operator's advice while you wait.
FAQ
How much water should I drink in hot weather?
The WHO suggests about 1 cup of water an hour and at least 2–3 liters (about 68–101 fl oz) a day in the heat. If you're working hard or exercising you'll need more, spread through the day, but NIOSH advises generally no more than 6 cups an hour.
Are sports drinks better than water in the heat?
For moderate activity lasting under 2 hours, NIOSH's advice is plain water. It suggests sports drinks with balanced electrolytes when sweating goes on for several hours, while the CDC suggests going easy on drinks high in sugar and sodium.
Should I avoid coffee and alcohol in a heatwave?
The CDC suggests limiting caffeine and alcohol in hot weather, and NIOSH advises people working in the heat to avoid alcohol and drinks with high caffeine or sugar. Water is the simplest choice for most of your drinks on a hot day.
What are the signs of heat exhaustion?
The NHS lists tiredness, dizziness, headache, nausea or vomiting, cramps, strong thirst, a high temperature, and heavy sweating with pale, clammy skin. Move the person somewhere cool and give them a drink; if they're not better within 30 minutes, call your local emergency number.
Sources
- CDC (2026). About Heat and Your Health
- CDC (2024). Protect Yourself From the Dangers of Extreme Heat
- CDC, NIOSH (2026). Workplace Recommendations: Heat Stress
- NHS (accessed 2026). Heat exhaustion and heatstroke
- World Health Organization (accessed 2026). Heat and health
- Institute of Medicine, National Academies (2005). Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate, chapter 4: Water
This article is general information, not medical advice. If you have a health condition or your doctor has given you a fluid limit, follow their advice.
