When the weather’s so hot that you break into a sweat just from stepping outside, much less doing anything active, taking in enough fluids to stay hydrated is a top priority. Water is the single largest part of your body it makes up about 60 percent of your body weight and 83 percent of your blood.
All that water keeps your blood flowing smoothly, regulates your body temperature, removes wastes efficiently, and lubricates and cushions your joints. But because your body is constantly losing water to sweat, breathing, urination, and bowel movements, your supply needs constant replenishment.
The warmer the weather and the more active you are, the more fluid you lose over the course of a day, and the more you have a drink to replace it.
How much water do you need to take in each day to replace the losses and keep your body functioning well?
There’s no simple answer to that question—no single reference value applies to everyone. The National Academies of Sciences, Engineering, and Medicine (the same agency that brings you other official nutrition standards) says that an adequate daily fluid intake is about 15.5 cups (3.7 liters) for men and about 11.5 cups (2.7 liters) a day for women.
That’s assuming a temperate climate and a fairly low level of activity. About 80 percent of the fluids most people consume each day come from water and other drinks. The rest comes from the fluids in foods, mostly fruits, and vegetables.
What it comes down to is the often-repeated advice to drink six to eight cups of water a day if you lead a fairly sedentary life in a temperate climate. That amount is the bare minimum, however. If you’re active or exercising hard and/or if the weather is very warm, you need more a lot more than the basic minimum amount. How much more? As much as you can manage comfortably, as often as you can.
A good approach is to drink plenty of water before going out in hot weather or beginning your exercise session, drink plenty more again while you’re out or exercising, and then have even more water once you’re out of the heat or have finished your workout. If you start out hydrated and stay that way, you’ll have a better session. You’ll be able to work harder for longer, and you’ll recover faster.
Don’t stop there., though. In hot weather, keep drinking for the rest of the day and into the evening to stay hydrated. (If you have to get up in the night more than once to use the bathroom, stop drinking after 8 p.m., but only if you’ve been hydrating adequately all day long.) Don’t rely on simply feeling thirsty or not being sweaty.
By the time you feel the need for a drink, you could already be on the way to dehydration. And if you’re not sweaty, it could be because the air is very hot and dry. You might still be sweating but not really be noticing it, and you’re still losing fluid in other ways. If you’re an older adult, your sense of thirst is probably diminished and is even less reliable as a guide to staying hydrated; ditto for your ability to sweat.
The best way to tell if you’re drinking enough is to check the color and volume of your urine. When you’re optimally hydrated, you produce a lot of urine that’s a clear, light yellow color or even colorless.
When you’re drinking enough to have light yellow urine, you’re putting less strain on your kidneys and circulatory system and have enough fluid in your body for all your other systems to work well. The lower the volume and the darker your urine, the less hydrated you are. When you’re consistently on the dehydrated side, you tend to feel tired a lot and you’re more likely to develop kidney stones, urinary tract problems, and constipation.
When the weather is hot, stick to plain tap water. It’s free, it’s easily available, and it doesn’t have any calories. It also doesn’t have any sugar, artificial sweeteners, caffeine, or carbonation—all additions that can make you feel full and keep you from drinking enough.
Skip the bottled water if you can. The U.S. has one of the safest water supplies in the world you almost certainly don’t need to buy expensive, environmentally damaging bottled water. (If you have concerns about your drinking water, contact your local water supplier and ask for the most recent annual drinking water quality report.)
The exception to the tap water rule is if you’re exercising hard in hot weather (for more than an hour) and sweating a lot. Tap water will help, but you might want to rehydrate with a sports drink that contains electrolytes.
These drinks help replace sodium, potassium, and magnesium lost through sweating. You can make your own sports drink by combining a quart of cold water, green tea, or herbal tea with half a cup of orange juice and a quarter teaspoon of salt. Throw in some fresh ginger or herbs for added flavor; sweeten with a pinch of stevia or a spoonful of honey if you wish.
Just as important as staying hydrated in hot weather is recognizing the signs of dehydration from not drinking enough. Signs of mild dehydration include feeling very thirsty, having a dry or sticky mouth, muscle cramps, nausea, a headache, and dark yellow urine.
As you get more dehydrated, you start to feel irritable or confused, you get dizzy, have a rapid heartbeat, feel tired and listless, and may even pass out.
If you notice signs of dehydration, get water or a sports drink into your body as soon as possible. If you’re only mildly dehydrated, drinking at least 8 ounces should help you feel better quickly; keep drinking until your urine is again pale yellow.
More severe dehydration may need to be treated with intravenous fluids in the emergency room. That can really slow down your summer fun-avoid dehydration by drinking often all-day long.
I believe that restoring optimum function is a major component of eliminating pain and preventing injury. Staying hydrated is key.
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Inpost Image Credit: Essmc.com, Shutterstock.com
 The National Academies, Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate, 2004. www.nap.edu.
 Find community water quality information at ofmpub.epa.gov.
 Y Sterns RH. Maintenance and replacement fluid therapy in adults. uptodate.com
 Kenefick RW, Cheuvront SN, Leon LR, O'Brien KK. Dehydration and rehydration. In: Auerbach PS, Cushing TA, Harris NS, eds. Auerbach's Wilderness Medicine. 7th ed. Philadelphia, PA: Elsevier; 2017:chap 89.