Its hard to tell if you are really drinking the recommended eight 8oz glasses of water. So my mom and I used old juice bottles to make these day's worth of water bottles.
We did the lines by measuring 16oz of water and pouring it in to the bottle and making the mark on the side. You continue adding 16 oz of water for each mark. The final mark at the top is your fill to line.
I have been trying this out today. Its almost noon and I have drank almost to the noon mark. Yeah I'm on track for my water intake.
You could buy a fancy bottle with a squirt top and do the same thing but today we are recycling.