How to stay hydrated in hot weather

2026-10-30

In hot weather, drink regularly through the day instead of waiting until you're very thirsty, carry water with you, and check that your urine stays light yellow. If you're working or exercising in the heat, a good rule from the US National Institute for Occupational Safety and Health (NIOSH) is about one cup (8 fl oz, 250 ml) every 15–20 minutes, but no more than about 48 fl oz (1.4 liters) per hour. Just as important: keep cool, avoid the hottest hours, and know the signs of heat exhaustion and heatstroke, because drinking alone won't protect you from overheating.

Why heat raises your water needs

Your body cools itself mainly by sweating. In hot weather you sweat even at rest, and during activity sweat losses can reach 1–2 liters an hour or more. On top of that:

Humidity slows the evaporation of sweat, so you sweat more for less cooling.
Thirst lags behind. You can lose a fair amount of fluid before you feel really thirsty, especially if you're busy, older, or distracted.
Heat and dehydration amplify each other. Less fluid means less sweat and less blood flow to the skin, so your body temperature climbs faster.

The CDC's heat and health guidance recommends drinking water on hot days regardless of how active you are, carrying a bottle, and using urine color as a check: light yellow or clear usually means you're drinking enough.

How much to drink

There is no single number, because needs depend on your size, the temperature and what you're doing. Practical anchors:

At rest on a hot day: start from your usual daily goal (see how much water you need per day) and add a few extra glasses. Drink a glass with every meal and one in between.
Working or exercising outdoors: about 8 fl oz (250 ml) every 15–20 minutes, or roughly 24–32 fl oz (0.7–1 liter) per hour, according to NIOSH's hydration guidance. Small, frequent drinks work better than large amounts now and then.
The upper limit: don't drink more than about 48 fl oz (1.4 liters) per hour. More than that can dilute the sodium in your blood, which is its own medical emergency (see can you drink too much water?).
Afterwards: most people need several hours to replace sweat losses. Keep drinking through the evening, and eat a proper meal; food replaces the salt you sweated out.

What to drink (and what to limit)

Water is the best everyday choice. Cold water is fine and can be more pleasant to drink.
Food counts too: fruit and vegetables such as watermelon, cucumber and tomatoes add water. See water-rich foods.
Electrolyte drinks are useful for long hours of sweating, physical work, or long exercise; for most people on a hot day, water plus normal meals is enough. More in electrolytes: when do you need them?
Limit alcohol, and go easy on very sugary drinks and lots of caffeine. The NHS's heatwave advice recommends sipping cold drinks regularly and limiting alcohol, caffeine and hot drinks. Moderate coffee is fine for regular drinkers; see does coffee dehydrate you?

A practical plan for a hot day

Morning: drink a glass or two with breakfast. Check the forecast and plan outdoor tasks for early morning or evening.
Leaving home: take a filled bottle, and refill it whenever you can.
Midday: stay in the shade or indoors, especially between 11am and 3pm. Wear loose, light-colored clothing, a hat and sunscreen.
Every hour: drink something, even if you're not thirsty. Reminders help when you're busy.
If you're active: follow the 8 fl oz every 15–20 minutes rule, take breaks in the shade, and slow down.
Evening: keep drinking, eat a proper meal, and check your urine color.
At night: keep your bedroom cool: close blinds during the day and open windows when the air outside is cooler.

Getting used to the heat

Your body adapts to heat over about one to two weeks: you start sweating sooner, sweat more, and lose less salt in your sweat. Until then, you're more vulnerable. Workplace heat guidance in the US uses a "20% rule" for new workers: no more than 20% of the usual time in the heat on the first day, increasing by no more than 20% each day. The same idea applies to sport: on the first hot days of summer, or on holiday in a hotter climate, shorten and slow down your workouts.

Know the warning signs

Heat exhaustion

According to the NHS, signs include headache, dizziness, nausea or vomiting, heavy sweating with pale, clammy skin, cramps, a raised temperature, intense thirst, tiredness and irritability. If someone shows these signs:

Move them somewhere cool.
Loosen or remove unnecessary clothing.
Give them plenty of water to drink; a sports drink or oral rehydration solution also works.
Cool their skin with cool water and fan them; cold packs around the armpits or neck help.

They should start to feel better within about 30 minutes.

Heatstroke: an emergency

Call 911 (or your local emergency number) if someone is still unwell after 30 minutes of cooling and fluids, or has signs of heatstroke: a very high temperature, hot skin that has stopped sweating, confusion or poor coordination, a seizure, or loss of consciousness. Keep cooling them while you wait. Don't try to give drinks to someone who is confused or not fully conscious.

Who's most at risk

The NHS and CDC highlight:

Older adults, whose thirst is weaker and who may take medicines that affect fluid balance. See hydration for older adults.
Babies and young children.
Pregnant people.
People with heart, lung or kidney disease, or taking several medicines. Don't stop or change medication on your own; ask your doctor if you should adjust anything in a heatwave.
People who work or exercise outdoors.
People who live alone. Check in on neighbors and relatives during a heatwave.

Let your tools do the remembering

On hot days the hard part is often simply remembering to drink. Water Tracker's reminders nudge you through the day and go quiet once you reach your goal, and you can log a drink from a Home Screen widget, with Siri, or on your Apple Watch without taking out your phone. If you mark yourself as active, the suggested goal is a bit higher; on very hot days, you can simply raise your goal for the day.

The bottom line

Drink regularly on hot days, before you're very thirsty, and watch for light yellow urine.
Outdoors and active: about 8 fl oz (250 ml) every 15–20 minutes, no more than about 48 fl oz (1.4 liters) per hour.
Water plus meals is enough for most people; electrolytes help for long hours of heavy sweating.
Avoid the midday heat, adapt over 1–2 weeks, and know the signs of heat exhaustion and heatstroke.

This article is general information, not medical advice. If you have a health condition, are pregnant or take medication, ask your doctor how much you should drink.