I finally got an answer from support that I had to drink whenever I was prompted by the app. This doesnt work for me because of my job. They say this is to prevent achievemints from being manipulated. Sorry but the app has to go. Impossible for me to drink a full glass of water on demand. I sip all during the day. If you drink like I do then it will be wasted money.
Loopy2005 about Water Habit - Drinking Water Reminder and Tracker