The app works fine I guess but I played with it and my takeaway was WHY?!?!? Why do I need an app to tell me Im thirsty? If I need a reminder, set a reminder. And the amount of water it recommends is NOT backed by science (there is no consensus) so you may still be over or under hydrating!
KojoKenobi about Water Tracker by WaterMinder®, v3.1