The Thundering Good Today Book

I've been trying to find this book for ages! It was one of my childhood favorites. I remember reading it during Christmas vacation in probably 1971 or 1972. I felt very grown-up (just like Mom) reading it by candlelight in a Hawaiian White Ginger bubble bath (both the candle and bubble were Christmas gifts). Sadly, I'm not able to remember much about the book other than the time capsule experience of reading it. I've googled around a bit - I think the main character's name was Hadra or something that meant water - but I've not found it anywhere. I'd love to find a copy and reread today.