According to Cohen, it’s impossible to give everyone the exact same rule of thumb. But for some general guidance, she would say to drink half of your weight in ounces. So, for example, someone who weighs 150 pounds would want to drink around 113 ounces of water, which is about nine cups. 

It’s a bit more of a personalized calculation than an eight-cups-per-day standard, but don’t take it as gospel, either. Cohen says that number can totally vary depending on your lifestyle habits: “If you go on a ketogenic diet or a carnivore diet, you probably need around 75% of your weight in ounces, because it’s a dehydrating diet.” Or let’s say you have a thing for sweaty HIIT workouts: The more you sweat, the more fluids you lose, and the more water you’ll need to drink.  

Consequently, Cohen explains, you may need less water than others—don’t force yourself to gulp down gallons just to meet a certain threshold. “There’s this whole new thing with drinking a gallon of water a day, which is 16 glasses of water a day,” she says. “That may be fine for some people, but for a lot of people, it’s probably too much water. You can overdo it.”  

The bottom line? While you can follow a general quota, only you can know the exact ideal amount of water to drink daily. As Cohen notes: “The only way to know is to live in your body and know what it feels like.” 

https://www.mindbodygreen.com/articles/how-much-water-should-you-really-be-drinking-md-explains