Want to know how much water you are drinking in a day?
Drink from a measuring cup!
At the restaurant The Works, they serve their water in big measuring cups. Thanks to these cups, I now know that I drank a liter over the course of my dinner (2 of these cups = 1 L).
If you struggle to consume 2 L of water a day (the recommended amount for healthy adults) maybe a measured drinking device would help you keep track of the water you are consuming.