…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.
During summer, but working inside, I will easily drink 4 litres. Any temp above 22°C and I start to sweat, a lot. When we had a heat wave one year, around 38°C inside, the water was just running off my hands and soaking the laptop keyboard. Puddles on either side of track pad, and forming on the desk.