…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.
If it is water, but it has minerals in it, it’s not water
If it’s water, but it’s distilled, it’s not water
If it’s water, it isn’t.