I really feel for you and cannot imagine only a half litre per day.
He's a good dad, and those kids are lucky.
I Believe you set the Kids up to fail.Imposing a tight fluid limit without advising of some of the coping skills is a near guarantee of failure. Even if self-imposed.I force myself to allow ONLY one mouthful of any fluid at a time. And force myself to wait almost an hour if I want another. And I fail at this some times.I carry a shirt pocket full of Mint Life Savers. One can really help with a dry mouth.When all else fails, a small ice chip, or medium, or even a large one if I'm at home as we don't have anything smaller than cubes and I'm too lazy to try to bash them into smaller pieces.And besides, I'm THIRSTY!