What Are the Signs You May Be Dehydrated?

Garth Graham, MD, MPH, the director and global head of healthcare and public health at Google/YouTube and Google Health, and a cardiologist based in Fort Lauderdale, Florida, says that dehydration generally doesn’t sneak up on you. There are physical signs of dehydration, including headaches, fatigue, vomiting, and a flushed complexion, he says. Dehydration may also make you feel irritable and zap your energy, says Sean Hashmi, MD, a nephrologist with Kaiser Permanente in Woodland Hills, California. “The body is such an incredible machine that it has built-in mechanisms that allow you to know when you need more or less water,” Dr. Hashmi says. Staying properly hydrated will not only help you avoid those negative side effects, but it will likely help you feel better overall — improving your mood, boosting brain function, and preventing fatigue, Williams says.

1. Respond to Thirst When the Feeling Strikes

The No. 1 sign that you’re dehydrated? Thirst, says Lustgarten. She points out that it can be easy to get wrapped up in day-to-day activities and forget to respond to your thirst cues, but they’re your body’s way of “communicating with you that you need more fluids,” Lustgarten says. Keep a water bottle nearby and take a swig whenever thirst strikes. Better yet: Try to drink water regularly throughout the day so you never reach that level. “I like to remind people to carry a water bottle with them and refill it throughout the day,” Lustgarten says. You can try setting personal hydration goals, say by challenging yourself to finish the bottle before lunch and drink another one before you head home in the evening.

2. Assess the Inside of Your Mouth for Dehydration Symptoms

Another simple way to gauge how well hydrated you are is to check the moistness of the inside of your mouth, Hashmi says. “In medical terminology, we say, ‘Check the mucus membrane,’ but basically, it’s a simple way to check the inside of your mouth,” he says. “If it’s starting to get dry, you know you’re running low on water.”

That long-standing advice to drink eight glasses of water each day? Unfortunately, for most of us, that’s not going to cut it. “That amount is only a general guideline and may not be enough fluid intake in more dehydrating environments or situations,” Williams says. The exact amount that’ll be right for you depends on a few things, including age and activity level, Williams adds. Keep in mind that this is most important for highly active athletes, such as professionals. “Most of us who get to the gym a few times a week don’t have to be concerned about this,” Lustgarten says. To determine your sweat loss and hydration needs, Williams suggests weighing yourself before and after exercise. “Losing less than 1 percent of your body weight during a workout is optimal,” she says. “For every pound lost, at least 16 fluid ounces [fl oz] of water or an oral electrolyte solution should be consumed to rehydrate.”

5. Bring in Extra Electrolytes When Needed

Most of the time, drinking plain water is enough to fend off dehydration, Lustgarten says. But certain circumstances call for something more. Williams says to drink about 4 to 8 fl oz of a low-carb electrolyte-containing beverage every 15 to 20 minutes when exercising for more than an hour. Just check out the nutritional facts label first, because many of these drinks can be packed with calories and sugar, Lustgarten says. “If someone is going to the gym and really sweating it out, although they might benefit from a sports drink, we also want to be aware of how many calories that person is taking in in a day so they’re not canceling out the hard work they’ve done at the gym,” Lustgarten says. She says that many brands make a low-sugar or calorie-free version, and she advises reaching for those options when possible.

6. Drink More Water When You’re Sick or in Hot Weather

Hot weather is also a clue that you need to increase your water intake. “If it’s hot outside, it’s always better to have more fluid,” Hashmi says, though he adds, “it’s really hard to have a formula for how much to drink.” It depends on factors like your body mass and how much you sweat.

7. Think Beyond Plain Water to Help Stave Off Dehydration

Lustgarten recommends water as the first choice when looking to rehydrate. Not a fan? No worries. “When it comes to hydration, all liquids count,” Hashmi says. “That can include coffee, juices, tea, and water.” You can add seltzer and carbonated water to the list, too, Lustgarten says. Just know that sweetened juices and teas will never beat out plain water in the healthfulness competition.