This screen allows you to keep track of water glasses you consumed.
Simply tap a water drop icon to indicate a glass consumed.
It is up to you to decide what is the size of a glass. In the US the most common size is 8 oz, or about 236ml. Outside of the US, the most common size is considered to be 200ml.
You can navigate between dates by tapping the arrows at the top part of the screen. To quickly return to Today's date, tap on the date.