If it feels harder to function during a humid Houston heatwave, that's because it is. Humidity makes your body work harder to cool itself, meaning you lose fluids and electrolytes more quickly through sweat. We explore how to stay hydrated in humid weather, so you can enjoy fun in the sun safely.
Why is it difficult to stay hydrated in humid weather?
We all struggle to stay hydrated in humid weather since moist air slows evaporation.
"Evaporation is the engine of sweat-cooling," says Sharon Mendez, a primary care certified physician assistant at Houston Methodist. "Once relative humidity climbs above around 60%, evaporation rate falls sharply."
Mendez affirms that our bodies must work harder in humid weather — the body's core temperature can rise faster, the heart rate climbs and our perceived exertion spikes as we try to stay cool.
"Your sweat keeps forming but can't evaporate fast enough to pull heat off the skin, so you are losing fluid continuously, and you get less cooling for every drop you lose," Mendez says. "The body then sweats even more to compensate, accelerating dehydration."
How much water does the average adult need in hot, humid weather?
We always want to strike a balance with hydration, where we drink enough to stay hydrated without overdoing it and causing excessive bathroom trips. Each of us has unique hydration needs based on factors such as our age, gender, current health and any medications. Generally, men need about 3.7 liters of fluid per day, and women need 2.7 liters of fluid. This includes all fluids, including those found in our food.
Sweating is another factor that affects how much water we'll need. To stay hydrated during a typical Houston summer day, you need to add around 0.5 to 1 liter to what you normally drink, according to Mendez.
However, if you're working outside for long periods, you'll need to consider the timing of your beverages.
"If you're outside working or exercising for over an hour, you'll want to drink 8 ounces of water every 15 to 20 minutes, or about 24 to 32 ounces an hour," Mendez says. "But it's important to not overhydrate — you don't want to drink more than 48 ounces in an hour. Doing so could cause you to dilute the sodium and electrolyte levels in your blood, which can lead to headaches, nausea and confusion, and can even lead to serious complications such as seizures and coma."
RELATED: Can You Drink Too Much Water During Exercise?
Can you 'pre-hydrate' before a day spent outside?
The best offense is a good defense, as the saying goes. If you know you're going to be outside during a blistering, humid day, you can be mindful and drink fluids before picking up your keys to go out the door.
"The best way to prepare your body for a day out in the heat is to drink about 2 to 3 cups of water (0.5–0.7 L) about two to three hours before heading out," Mendez says. "You'll want to drink another half cup to 1 cup every 15 to 20 minutes once you're out in the heat."
Mendez suggests sticking to the 15-20 minute rule during the peak midday heat, between 11 a.m. and 4 p.m., and slowing your water intake before bed.
When do you actually need electrolytes?
Electrolytes are essential minerals our bodies need to function optimally, including sodium (salt), potassium, calcium, chloride, magnesium and phosphorus. They play crucial roles in everything from regulating our blood pressure and supporting nerve and muscle function to balancing the fluid levels in our cells. When our electrolyte levels are low, it becomes harder for us to maintain proper hydration. So we may be drinking water, but the body will have trouble absorbing it.
"If you're outside for longer than an hour engaging in strenuous work or exercise, or if you notice signs of being a 'salty sweater,' you will need to replenish your electrolytes," Mendez says.
How do you know if you're a salty sweater, meaning you sweat out salt? If you've ever noticed white streaks on your clothes (and no, we're not talking about deodorant streaks), your sweat may have a high concentration of salt. Other signs you're sweating out salt can be that your sweat actually tastes salty or burns your eyes. You may even crave salty foods after exercise or being out in the heat.
So how can you quickly re-up your electrolytes? Sports electrolyte drinks, energy gels and electrolyte tablets and powders are often thought of as fast-track products to replenish electrolytes — and they are — but you could also take a break to eat your electrolytes with a snack or well-balanced meal. Foods high in potassium and magnesium can be great options, including bananas, avocados, citrus fruits and even watermelon.
Around 20% of your daily fluid intake should come from foods, and some fruits and veggies pull double duty by helping you refill your electrolytes and stay hydrated. Some foods that are high in water content and electrolytes include watermelon, which is 92% water, as well as oranges and grapefruit, both of which are 88% water.
Should you drink alcohol in the heat?
Whether it's beach outings, pool parties, music festivals or baseball games (not all stadiums have AC like Houston does), summer offers many reasons to celebrate with your favorite alcoholic drinks. But should you partake when heat and humidity skyrocket?
"Alcohol is a mild diuretic, and it dulls your perception, so you can start missing cues that you're thirsty, or your body temperature is rising," Mendez says. "It's better to not drink in this type of weather, but if you're going to — match every alcoholic drink with at least the same volume of water. No exceptions."
Mendez suggests sticking to lower-alcohol options (think low-ABV beer and spritzers) if you do choose to drink. Should you begin to feel lightheaded, stop immediately.
Who is most at risk of dehydration in hot, muggy weather?
While staying hydrated is challenging for most of us in this type of weather, certain populations are at a higher risk due to age and other circumstances.
Outdoor workers
Individuals whose careers require them to be outdoors in the heat for extended periods are at the highest risk for heat-related complications. The Occupational Safety and Health Administration (OSHA) recommends that workers should drink eight ounces of water every 15 to 20 minutes, no matter if they feel thirsty or not.
"Our thirst cues aren't always reliable, and people often overlook the early signs of dehydration," Mendez says. "The mouth or lips become dry, a dull headache can set in, or we can feel fatigue, lightheaded, or we notice muscle cramps or darker urine."
The agency also recommends that employers encourage workers to keep a sealable bottle of cold water in their work area and provide electrolyte products. Additionally, they should maintain a cool, shaded rest break location for those completing sweat-inducing tasks for extended periods.
"It's important to take breaks if you're doing any kind of labor in the heat," Mendez says. "Whether it's our career or we're just doing chores outside, we may want to 'push through' our thirst cues to finish our task or job quickly. That's when we're more at risk for heat illnesses when we try to push through the early signs of dehydration."
Younger children
Children younger than age four can become dehydrated quickly because their bodies have a larger skin-surface area compared to their body mass, which can make them absorb heat faster.
"Younger children rely on their caregivers to offer them fluids, so it's important to be able to spot the signs that a child is thirsty," Mendez says. "You can give children bright, personalized cups that can help cue you to refill their water or freeze a combination of fruit juice and water in an ice mold to make hydrating a fun treat in the heat."
Older adults
"Older adults can be at more risk because our thirst signals, kidney function and ability to conserve water can decline as we age," Mendez says. "Plus, certain medications can speed up fluid loss and blunt our body's heart rate and sweat responses."
Mendez suggests older adults work with a primary care clinician for a personalized hydration plan.
"Ask your clinician what to drink and how much you should drink on hot days," Mendez says. "Since they know your medical history and medication list, they can suggest when and if you should be drinking plain water or low-sodium electrolyte drinks to make sure you're adequately hydrated without complications."
In general, Mendez says that caregivers for older adults can aim to offer their loved one six ounces of water each waking hour unless indicated otherwise by their loved one's provider.
"Caregivers can monitor for dehydration by looking at their loved one's urine color and mental status," Mendez says. "Urine should look like pale lemonade — we call this the lemonade test — any darker than that you or your loved one needs fluids. Confusion and dizziness are usually earlier signs of dehydration than thirst, so you'll want to act fast if you notice these signs."
People with heart, kidney or endocrine disorders
People living with certain conditions — including heart problems (especially heart failure), chronic kidney disease (CKD) and diabetes — can walk a tightrope between fluid overload and dehydration.
"Many people with heart disease take diuretics that increase their urine output or medicines that deplete fluids, such as ACE inhibitors or Angiotensin II receptor blockers for blood pressure management," Mendez says. "Additionally, heat causes blood vessels to dilate, which can lower blood pressure, and weaker hearts will struggle to compensate, which raises the risk of arrhythmia and fainting."
Related: Medications That Don't Mix Well With the Sun or Heat
Those with chronic kidney disease (CKD) also face unique hydration challenges in the heat. Damaged kidneys can't quickly adjust urine volume or electrolytes, and some individuals with CKD must limit their fluids to prevent fluid buildup in the body. This can make catch-up drinking tricky once someone is showing signs of dehydration.
"Repeated exposure to excessive heat and dehydration together can trigger acute kidney injury and further CKD progression," Mendez says. "People with heart failure or CKD should weigh themselves in the morning and the evening, and if they gain two pounds or more in a day, they should call their provider."
Common complications of diabetes can increase the risk of dehydration during a heatwave for individuals living with the condition.
"When blood sugar levels are high, it pulls water into the urine which causes frequent bathroom trips," Mendez says. "Plus, nerve damage called autonomic neuropathy can blunt a person's thirst or sweat. Diabetes medications, such as SGLT-2 & GLP-1 drugs, can add extra fluid loss or thirst suppression on top of that."
Stay consistent to stay hydrated in the heat
Life goes on, and we can't escape summer in Houston. Mendez says that consistency is crucial to stay hydrated so you can function optimally in the heat. Mendez suggests the 1-2-3 bottle rule to keep yourself steadily hydrated during the day: try to drink one refillable 16.9-ounce bottle by breakfast, two bottles by lunch, and three by dinner.
"Be consistent and drink steadily throughout the day, not desperately trying to catch up when you start to feel thirsty or dehydrated with a headache," Mendez says. "In Gulf-Coast humidity, aim for 80–100 ounces on a typical summer day — and bump it up any time you're sweating."
