Help for remembering a fantasy book with water and fire people at war

I recently remembered a book I read end 90 beginning 2000, but was very probably older than that, I thought I could find it quickly, but R.R.Martin is overshadowing all other research...

The book is about two society, one of "fire" people, who lives in a desert and fear water (I don t remeber if they drink very little or if water is just a poison to them, but it s bad for them), and "water" people, who can t live if too far from water. The two society are at war for some reason, and a "fire" boy end up loving a "water" girl.

I also remember that a anime movie was made based on this book, but was more lighthearted and centered around the two lover.

Thanks for any help.