Hydration in Hot Weather: Staying Safe in the Heat

How Heat Affects Fluid and Electrolyte Loss

When you’re active in hot weather, your body sweats to stay cool. Sweat is mostly water, but it also contains electrolytes—especially sodium and potassium—that help your muscles and nerves function. The hotter and more humid the day, the more you sweat, and the more fluid and electrolytes you lose.

Humidity makes the problem worse. In humid weather, sweat lingers on your skin and evaporates more slowly, so your body has a harder time cooling down. It keeps sweating, which leads to even greater fluid loss.

Sources: The Texas Heart Institute

Who Is Most Vulnerable to Heat-Related Illness

Anyone can develop a heat-related illness if they’re active in the heat long enough, but certain people face higher risk. This includes outdoor workers, athletes, older adults, young children, and people with chronic health conditions. Also, people who are not yet acclimated to hot weather—like those starting a summer job or traveling to a warmer climate—are more susceptible.

If you fall into a higher-risk group, take extra care to plan your activities, pace yourself, and watch for early signs of heat illness.

Sources: The Texas Heart Institute

Adjusting Water and Electrolyte Intake in Hot Weather

As a general guide, secondary sources summarizing NIOSH/OSHA recommendations advise drinking about 8 ounces of cool water every 15 to 20 minutes while you’re exposed to heat—roughly one quart per hour. However, don’t exceed about 48 ounces (1.5 quarts) of water per hour, because drinking too much plain water without electrolytes can lead to a dangerous condition called hyponatremia, where blood sodium levels drop too low.

For shorter periods of work or activity—under about two hours in moderate conditions—cool drinking water is usually enough. For longer sessions or heavy sweating, water alone is not sufficient. You need to replace electrolytes, especially sodium and potassium, through a balanced electrolyte drink or salted foods.

Relying on thirst is not a good strategy. By the time you feel thirsty, you may already be mildly dehydrated. Regular hydration breaks are safer, especially when you’re busy or distracted.

• Drink about 8 ounces of cool water every 15–20 minutes during heat exposure.
• Limit total water intake to about 48 ounces per hour to avoid overhydration.
• For shifts or activities lasting 2 hours or more, add an electrolyte drink or eat salty snacks.
• Don’t wait until you’re thirsty; schedule hydration breaks.

Sources: Enviroguard, Hydration Depot, Sentry Road

Recognizing Heat Exhaustion vs. Heat Stroke

Heat exhaustion happens when your body overheats due to excessive fluid loss and struggles to maintain a safe internal temperature. Symptoms may include heavy sweating, a rapid pulse, dizziness, nausea, and cool, clammy skin despite the heat. This is a warning sign that you need to cool down and rehydrate.

Heat stroke is a life-threatening emergency. It occurs when the body’s cooling system fails, and core temperature rises above 103°F. If you suspect heat stroke, seek immediate medical help. While waiting for help, move the person to a shaded or air-conditioned area, remove excess clothing, and try to cool them down.

• Heat exhaustion: heavy sweating, rapid pulse, dizziness, nausea, cool/clammy skin. Move to shade, remove extra clothing, and hydrate with water or an electrolyte drink.
• Heat stroke: core temperature above 103°F, confusion, possible loss of consciousness. Call for emergency medical help immediately.

Sources: The Texas Heart Institute, Salt of the Earth

Practical Hydration Tips for Outdoor Activity

When you’re out in the heat—whether working, hiking, or playing sports—plan ahead. Carry more fluid than you think you need, and choose a drink that matches the length and intensity of your activity. For short, light outings, water may be fine. For longer or intense sessions, include electrolytes.

A good rule is to take hydration breaks every 15 to 20 minutes, even if you don’t feel thirsty. Use your urine color as a rough guide: pale yellow usually means you’re well hydrated. Dark yellow suggests you need to drink more.

• Start your day well hydrated, not just during activity.
• Bring a reusable bottle and refill it often.
• If you’re hiking, plan water sources or carry extra. On long hikes, an electrolyte drink can help replace what you lose in sweat.
• Avoid alcohol, which can increase fluid loss.
• Wear light, breathable clothing and take breaks in the shade when possible.

Sources: The Texas Heart Institute

When to Stop Activity and Seek Medical Help

If you or someone else shows signs of heat exhaustion—like dizziness, nausea, or heavy sweating—stop activity, move to a shaded or air-conditioned spot, and remove excess clothing. Hydrate with water or an electrolyte-rich drink. If symptoms don’t improve quickly, seek medical attention.

Heat stroke is a medical emergency. Call 911 or get to an emergency room immediately if someone has a high body temperature, confusion, or if they lose consciousness. Heat stroke can be fatal if not treated quickly.

• Stop activity and cool down at the first signs of heat exhaustion.
• Seek immediate medical help if you suspect heat stroke.
• Never leave a person with heat stroke alone; get professional help right away.

Sources: The Texas Heart Institute, Drink LMNT