…because the shape of the water bottle isn’t uniform either. Part of my new year’s resolution is to drink 4 liters of water per day, so I spend a lot of time looking at those lines. Edit: 4 liters is a lot, but appropriate for my size and activity level. Without conscious consideration I don’t drink enough water. It looks blue because the bottle is blue.
The mayoclinic page I linked said the 3.7 liters recommendation comes from the U.S. National Academies of Sciences, Engineering, and Medicine. But yeah, even if it’s 3 liters after you knock off the 20% you get from food intake, that’s a lot of water.
Was not a recommendation, but an observation on how much people seem to get. National academy of medicine also recommends drink when you’re thirsty.