…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.
4 liters of water per day is completely fine if you are not absolutely sedentary in a cool climate.
(The following is for a healthy male, who requires the most generally)
Average adult in a temperate climate needs 3.7L according to mayo clinic
harvard says a minimum of 3.1L per day
Most people are pretty dehydrated in general. Your piss isn’t supposed to be bright yellow.
BBC summarized some journal papers that said that most adults are 1-2% dehydrated. Human thirst mechanisms also degrade as we age, not to mention “nurture” factors like people not drinking enough water when they are young, so their thirst mechanisms are already skewed towards too little water. Also hunger and thirst mechanisms are tied together so dehydrated people may overeat more as their body tries to get more water through food (also contributing to the huge rise in obesity)
There are a variety of unpleasant problems that come from drinking too little water, drinking too much water (within reason, not 12L per day) has the side effects of good kidneys and pissing more often…
Of course, a 140cm person won’t need 4 liters, but a 2m tall person who goes to the gym may need 5+.