Is the “8 glasses a day” rule accurate?

It’s a reasonable rough average, but actual needs vary a lot based on body weight, activity level, and climate. A 50 kg person and a 90 kg person don’t need the same amount of water — this calculator adjusts for that.

Does this include water from food and other drinks?

No, this estimate is for plain water intake specifically. Roughly 20% of daily fluid needs are typically met through food, so you may need slightly less plain water than shown if you eat a lot of fruits and vegetables.