“Fluid needs can also be altered by an individual’s body mass and body composition,” says Ouldibbat, who points out that the Academy of Nutrition and Dietetics bases its recommendation on a person’s weight: “It recommends 30 to 35 milliliters of fluid a day for each kilogram that a healthy adult weighs. Therefore, for a 150-pound (68.2 kg) individual, fluid needs would be 70 to 80 ounces.” This calculation doesn’t separate out water intake from food, so if you’re eating lots of fruits and vegetables with a high water content, the amount of water you need to drink could be lower.
But, she explains, there are instances where weight-based recommendations may not apply, such as in cases of obesity, when it is crucial to use clinical judgment. The same applies to those on the other end of the spectrum. “If an individual is underweight or malnourished, a higher ‘ideal’ body weight may be used to accurately quantify fluid needs,” says Ouldibbat.
Another thing to pay attention to is how you feel. Obviously, if you’re thirsty, drink more water. But if it seems you need an excessive amount to quench your thirst, this could be an indication that something is up; a doctor or nutrition expert can help with specific questions.
Your water intake needs can change daily.
To complicate matters, and prove that there’s no hard and fast amount of water that you need each day, Ouldibbat says, “fluid intake goals can change daily based on your activity level, any losses such as sweating, and the season.” In short, the more you sweat—in which you lose water—the more water you’re going to need to drink. And often your body will tell you this without your having to think about it because you’ll naturally feel more thirsty.
How much you need to drink is also influence by age, health, and life stage. “Increased water intake is typically needed during pregnancy and breastfeeding,” says Bartlett. Ouldibbat points out, “Fluid needs will also increase as individuals approach geriatric age.” And Barlett says other reasons you may need to drink more water are if you’re sick (there’s a reason doctors recommend drinking lots of fluids when you’re under the weather), have certain health conditions, are taking certain medications, or are experiencing diarrhea.
What about other drinks like coffee, tea, soda, juice, etc.?
If you’re a Diet Coke fiend like I am (just one a day is a nice little treat, right?!), it actually counts toward your daily fluid goal. Caffeine does have a diuretic effect, increasing urination, but per the Mayo Clinic, most research has shown this effect is negligible. But caffeine is technically a drug, and limiting your intake is often the healthiest choice. And of course, sugary drinks have empty calories. Ultimately, Ouldibbat and Barnett stand by water being the best choice for staying hydrated.
How to tell if you’re dehydrated
In addition to the obvious sign of feeling thirsty, there are some other ways to tell whether you’re getting enough water. Ouldibbat recommends looking to your skin for certain indicators. “Pinch some of the skin on the top of your hand; if the skin immediately bounces back, you are likely hydrated.” Dehydrated skin, however, “will take a bit to return to normal. The more hydrated skin is, the more elastic it is,” she says.