I know... Another "trick", and I really didn't want to use another trick, but maybe that will help me get our relationship back on track:
I wil get her a special bottle, which will be hers to drink when she is at home. There will be like 0,7 L water in there (she drinks some water at school + breakfast milk etc, so it should be all her fluid needs for the day). There will be tons of benefiber in there. And it will be her responsibilty to drink it somehow during the day. Plus, the other positive things I said.
And sorry for not helping, Eco Goddess. I don't know, but I hope other people will be able to help.