The most official, science-y answer comes from the National Academies of Sciences, Engineering, and Medicine. They say a healthy adult male should aim for about 3.7 liters (or 15.5 cups) of total water per day. For women, they recommend around 2.7 liters (or 11.5 cups).
But wait—before you start chugging like a camel at an oasis, know this: total water includes what you get from food. Fruits, veggies, soup, and even that morning coffee count. You don’t need to live inside a fire hose.
Why Not Just “Eight Glasses”?
That old “8x8” rule (eight 8-ounce glasses) is a great starting point, but it’s a little like saying all shoes are size 9. It fits some people perfectly, and others are left with blisters. Your needs depend on your body, your activity, and the weather.
If you are a sweaty mess after a run, you need more. If you live in a cool, rainy climate and sit at a desk all day, you need less. Your body is not a one-size-fits-all water bottle.
