We've all heard we should drink eight glasses of water a day. But the advice isn't based on scientific evidence, and for some people it may be flat out wrong, report researchers in Harvard Health Letter.
They conclude that 30–50 ounces of fluid intake a day is ideal, and that works out to more like four to six (8-ounce) glasses a day. Note the word "fluid:" It doesn't have to be water to hydrate, reports CBS News. "It's really about fluids in general," one doctor in Cleveland says. "Doesn't necessarily have to be water. Lettuce, spinach, fruits in general, soups ... those are all things that are going to have a lot of water in them as well." (Of course, Americans may not be getting a ton of help from fruits and vegetables: Per a new CDC report, just 13 percent of adults eat the daily recommended amount of fruit; for vegetables, just 9 percent of adults, LiveScience reports.)
The piece in Harvard Health Letter also specifies that the water shouldn't be consumed all at once. "It’s important to stay hydrated gradually, throughout the day." To do that, it recommends taking fluids "at meals, with medicine and socially."
The Mayo Clinic suggests that while eight glasses is something of a myth, it lines up pretty well with recommendations by the Institute of Medicine, which suggest 3 liters of beverages a day for men and 2.2 for women, where all beverages count toward one's fluid intake.
Also important, especially if you're in the middle of a heat wave? Paying attention to signs of dehydration, which include dizziness, weakness, heart palpitations and dark urine.
(No one knows where the eight-glass water myth comes from, but it's not the only one floating around.)