How Much Water Do You Actually Need?

For most young, healthy people, the best way to stay hydrated is simply to drink when you’re thirsty, Dr. Topf said. (Those who are older, in their 70s and 80s, may need to pay more attention to getting sufficient fluids because the thirst sensation can decrease with age.)

And despite popular belief, don’t rely on urine color to accurately indicate your hydration status, Dr. Hew-Butler said. Yes, it’s possible that dark yellow or amber urine could mean that you’re dehydrated, but there’s no solid science to suggest that the color, alone, should prompt a drink.

One popular notion is that drinking beverages with caffeine or alcohol will dehydrate you, but if that’s true, the effect is negligible, Dr. Topf said. A 2016 randomized controlled trial of 72 men, for instance, concluded that the hydrating effects of water, lager, coffee and tea were nearly identical.

But in reality, most healthy people who blame feeling ill on being dehydrated may actually be feeling off because they’re drinking too much water, Dr. Hyndman speculated. “Maybe they’ll get a headache or they’ll feel bad, they’re thinking, ‘Oh, I’m dehydrated I need to drink more,’ and they keep drinking more and more and more water, and they keep feeling worse and worse and worse.”

If you drink at a rate beyond what your kidneys can excrete, the electrolytes in your blood can become too diluted and, in the mildest case, it could make you feel “off.” In the most extreme case, drinking an excessive amount of water in a short period of time could lead to a condition called hyponatremia, or “water intoxication.” “This is very scary and bad,” Dr. Hyndman said. If the sodium levels in your blood get too low, it can cause brain swelling and neurological issues like seizures, coma or even death.