Everyone has heard the advice to drink eight 8-ounce glasses of water every day. Is it really that simple? Is that amount supported by scientific evidence? Well, actually, no and no. How much water you need depends on a lot of things, including your health, your activity level, and the climate in which you live.
Our bodies are made up of about 60% water and every organ system depends on it to function correctly.
We lose water naturally thorough our breath, sweat, urine, and bowel movements. If we don’t replenish this supply by taking in enough water through beverages and food, we can become dehydrated.
So how much water does the average, healthy adult, living in a moderate climate need? The institute of Medicine (IOM) set the adequate intake (AI) for total water for men at 3.7 liters, or about 15.6 cups per day. That sounds like a lot, right? It’s a little confusing. “Total water” includes all water contained in food, beverages and drinking water (the total amount of water in everything we consume). For women, the AI for total water is 2.7 liters, or about 11.4 cups. Remember, that includes everything we consume. It turns out that the food we eat, on average, contributes about 20% of one’s total water intake for a given day. Think how juicy a tomato is. Many fruits and veggies are 90% or more water, by weight. A vegan is going to get a lot more water in their food than a meat eater.
So, for total beverages, the IOM set the AI for men at about 13 cups per day and for women it’s about 9 cups. Notice the word “beverage”. That means all fluids count, not just water. Yes – even caffeinated beverages like coffee, tea, and soda count. Of course these beverages should not be the primary source of fluids for your daily intake. Water is still the best option. It’s calorie-free, caffeine-free, economical, and easy to obtain (and it doesn’t stain your teeth or feel sticky when you spill a few drops on the floor).
You may need to modify your fluid intake depending on how much you exercise, how hot and humid it is, if you’re pregnant or breast-feeding, or if you have other health concerns (e.g., you’ve got a history of kidney stones — ouch!).
Activity/Exercise – If you are doing something that makes you sweat, you need to drink extra water. For activity that lasts an hour or less, you need about 1.5-2.5 extra cups. Exercise that lasts longer requires more. How much depends on how long, type of exercise, and how much you sweat. During long bouts of very heavy sweat-producing exercise, consider drinking a sports drink that contains sodium. Also, drink extra fluid even after you’re done with the activity.
Weather – The hotter and/or more humid it is, the more you sweat and the more fluid you need to consume. Heated indoor air and high altitudes can also increase your fluid needs.
Health Issues – If you have a fever and/or are losing fluids through vomiting or diarrhea, you should drink more water and may benefit from beverages like Gatorade. Keep in mind, some health conditions may necessitate you limit your fluid intake. These may include heart failure and some types of kidney, liver, and adrenal diseases.
Pregnancy/Breast-Feeding – According to the IOM, pregnant women should drink about 10 cups a day and those who are breast-feeding should drink about 13 cups.
Age – Don’t rely solely on your thirst mechanism, especially if you are elderly. It is common that older folks don’t consume enough fluid throughout the day.
Generally, if you drink enough fluid so that you are rarely thirsty, your urine is very light yellow or colorless, and you excrete about 6 cups of urine daily, your intake is probably sufficient. If you are concerned about your fluid intake or have health issues, check with a Registered Dietitian or your physician. He or she can help you figure out the amount of water that is right for you.
Although rare, it is possible to drink too much water. When you have a lot of excess fluid in your system, you dilute your blood and your sodium, an important electrolyte, drops below normal levels. Marathon runners and people who take part in crazy radio stunts are at a higher risk for water intoxication because they drink large amounts of water at a single time. Under normal circumstances, accidentally consuming too much water is exceptionally rare.
So go grab a bottle of water and toast to your health. Cheers!
by Mary Ann Conroy, RD, LD
Adrien Paczosa is a Registered and Licensed Dietitian practicing in Austin, Texas and the surrounding counties.
She is the owner and founder of I Live Well Nutrition her Dietitian practice which started in 2007 and serves clients in the Austin, Texas area in two locations. Fearless Practitioners, the division of her business that offers training to dietitians and wellness professionals.