There's a city with a Sultan that has conquered another city by building a magical bridge from the nightmares of children. There's a pampered girl in the first city who is afraid she's going to be taken to dream, and a ragged boy in the second city who sells water because water is his route to magic.
This is a fantasy novel with an Arabian Nights feel. The two alternating threads don't come together -- though I suspect they will in the sequel. It's beautifully written, the characters are very real and it held my attention all the way through. But (and you knew there was a but coming) a few days after reading it it's kind of hazy, I can't recall the names, and what I remember most is the feel of the world and a memory of having enjoyed reading it. I'll have to re-read it when the sequel comes out in paperback.