With Log My Water you can log your consumed drinks and synchronize them through the Health-App!
At first you get an overview of your last entry, about the amount you drunk as well as at the time of your last entry.
You will also get an overview of the total amount of drunken water for the day.
You can then enter the amount of water you have drunk freely and synchronize it with the health app.
Only the unit of the liquid (e.g. ml or oz) must or can be adjusted.
Much thanks to /u/chefchip1965 on reddit for helping me out on this one!