Woman drinking a glass of water

The "8, 8 oz glasses of water a day" advice still holds true.

These days, we have so much to choose from to drink—soda, tea, coffee, juices, and sports, vitamin and energy drinks. Even though these drinks contain water, you still may not be getting enough fluids.

Dr. Irvin Sulapas, a primary care sports medicine physician and assistant professor of family and community medicine at Baylor,1 states that, “The rule of thumb is, if you’re thirsty, you’re already dehydrated. So keep well hydrated by drinking plenty of water, even before you begin your outdoor activity.”

Beware of liquids that make you lose fluids, like alcoholic beverages or drinks with caffeine, which cause more frequent urination. Don't count coffee, tea, soda, beer or other alcoholic drinks into the total amount of liquid you need to stay healthy and hydrated.2

The weight of water

Did you know two-thirds of your body weight is water? That means a 120-pound person carries 80 pounds of water.3

Everything in the human body depends on water. Your liver, heart, blood, brain, stomach—without water, none of these would work. Our blood is water-based, as are the cells that are the basic building blocks of everything we are.

According to scientists on the Mayo Clinic staff, the food we eat is good for about 20% of the water our bodies need each day.4 Even though some foods like tomatoes and watermelon have high amounts of water, you'd still have to eat a whole lot of them every day to get the same amount you’d get from 8 daily glasses of water.

Sweat: your body’s air conditioner

The Centers for Disease Control and Prevention says when our body temperatures go above normal (98.6 degrees Fahrenheit), our brains send out an alarm. This makes us sweat, which cools us down and protects vital systems like our hearts and brains. Like air conditioners, our bodies have built-in thermostats that help control temperature, and our sweat cools them. Whether it's from physical activity or just the weather, when we get hot, our bodies’ air conditioners kick in, and we start to sweat. So we need to drink lots of water.5

So how much do you need to drink?

Start with an 8 oz glass of water with each meal and an 8 oz glass between each meal. You're already up to 5 glasses a day, more than half of the 8, 8 oz glasses doctors from the Mayo Clinic staff say we need.6

Things you do can affect how much you need to drink

Exercise – When you exercise, be sure to drink plenty of water before, during and after exercise. One way to remember might be to think "2 + 2," which means to start adding to your body's water supply by drinking at least 2 cups of water 2 hours before you plan to play, work out or just be in hot weather.

Once you get going, plan to take a break and drink about 10 oz—that's 10 large gulps—from a water bottle every 15 to 20 minutes while you're exercising. And keep drinking after you finish.7 Remember: by the time your body says, "Hey! I feel thirsty," you may already be dehydrated.

Fruit and other snacks are another way to keep your body a little cooler. Peaches, oranges, watermelon and grapes help fill your stomach and top up your water level.8

Finally, don't forget that sometimes—like when you're swimming—you may not notice you're sweating. But you are, and you can still get dehydrated, so play it safe. Drink up!

Sickness – Your body needs extra water to flush out poisons in your system. More than ever, water is key for this. Your cells need all the help they can get to fight infection, and dehydrated cells can’t do what they need to do. If someone is throwing up, he or she needs to drink water in small sips every 10 minutes.9

Breastfeeding, pregnancy or long-term illness – All these mean big changes for our bodies, changes that can be very stressful. Talk to your doctor, because dehydration can cause distress to a system that's already working really hard.

Signs of dehydration10

Signs of mild dehydration—treat by drinking liquid in small sips:

  • Small amounts of dark yellow urine
  • "Dry mouth" and tongue with thick spit
  • Weakness
  • Lightheadedness
  • Headache
  • Cramping in the arms and legs
  • Deep breathing

Call 911 right away if you notice these signs:

  • Sunken eyes
  • Very fast pulse and breathing
  • Fainting
  • Crankiness
  • Cold hands and feet
  • Lack of energy
  • Coma
  • Dry eyes (no tears)

Material for this article was gathered from various sources including the Centers for Disease Control and Prevention (part of the U.S. Department of Health and Human Services), the Mayo Clinic, and the University of Illinois.

Links to various other websites from this site are provided for your convenience only and do not constitute or imply endorsement by Humana of these sites, any products or services described on these sites or of any other material contained therein. Humana disclaims responsibility for their content and accuracy.


  1. Dana Benson, “Thirsty? You're Already Dehydrated,” Baylor College of Medicine, last accessed January 15, 2021, https://www.bcm.edu/news/sports-medicine/thirsty-you-are-already-dehydrated, opens new window.
  2. “Dehydration,” Cleveland Clinic, last accessed January 15, 2021, https://my.clevelandclinic.org/health/treatments/9013-dehydration, opens new window.
  3. “Water in Diet,” MedlinePlus, U.S. National Library of Medicine, last accessed January 15, 2021, https://medlineplus.gov/ency/article/002471.htm, opens new window.
  4. “Water: How Much Should You Drink Every Day?,” Mayo Clinic, last accessed January 15, 2021, https://www.mayoclinic.org/healthy-lifestyle/nutrition-and-healthy-eating/in-depth/water/art-20044256, opens new window.
  5. “Press Release: The Centers for Disease Control and Prevention (CDC) Warns that Heat-Related Illness Could Rise This Summer,” Centers for Disease Control and Prevention, last accessed January 15, 2021, https://www.cdc.gov/media/pressrel/r010713.htm, opens new window.
  6. “Water: How Much Should You Drink Every Day?”
  7. Brenda Jacklitsch, “Keeping Workers Hydrated and Cool Despite the Heat,” NIOSH Science Blog, Centers for Disease Control and Prevention, last accessed January 15, 2021, https://blogs.cdc.gov/niosh-science-blog/2011/08/12/heat-2/, opens new window.
  8. “Guide on How to Be Hydrated—EAT Nature's Water,” Hydration Foundation, last accessed January 15, 2021, https://hydrationfoundation.org/guide-on-how-to-be-hydrated-eat-natures-water/, opens new window.
  9. Benjamin Wedro, “Dehydration Facts,” MedicineNet, last accessed January 15, 2021, https://www.medicinenet.com/dehydration/article.htm, opens new window.
  10. “Dehydration Facts.”