What a find! Amazon's correlation algorithms triumph and find a book that is a cut above the typical YA dystopia.
It's also going to be a difficult one to review without spoilers - there are several classic books I'd love to compare it with - favourably - and I can't, because that would give the game away.
In an interim post, I referred to the book as a trap closing. I read the book knowing almost from the start that some key characters were not going to make it to the end. The hints are strong, they are there for the reader to pick up, and if you miss those, you'll miss a lot of the tension.
The novel is set in a future time, post ecological failure, and a lot of technology has been lost, and its incomprehensible remnants are to be found in landfill sites. Here the two protagonists find hints that some of the world might not be so bleak, beyond the borders of a thinly-disguised Chinese hydraulic empire. If you're not familiar with the term - see http://en.wikipedia.org/wiki/Hydraulic_empire .
Being set in a true hydraulic empire, there is very little chance of internal rebellion succeeding - the very stuff of life is controlled by the elite - only a sufficient alternative supply can power a rebellion. Water crime is punished by death. The novel shows how these two combine to create intolerable pressure on ordinary people to become complicit in acts that they would ordinarily find abhorrent - it is a strength that the characters in the novel are flawed and anguished, rather than entirely virtuous or entirely evil.
Thus the novel builds its tension not through action, but by balancing the need to escape to discover if the lost lands have recovered, and the need for slow, careful preparation, limited also by the slow pace at which information about the lost lands can be uncovered. Against this backdrop, the military steadily increase their oppression of the populace, driving collaboration and betrayal through the need for water. You can see the trap closing, yet you can also see why the protagonists are forced to remain within the jaws 'just a little longer, then we'll flee'.
The slowness of the novel might be a sticking point for some - it took a while for it to become apparent where the novel was going. The novel is quite short, too. It feels like you're almost at the halfway mark before the journey-pattern becomes defined.
Technology thoughts. Perhaps a bit too pat, the way the CDs and the technology to play them get unearthed. The pods - used for sending messages - it took a while for me to understand the rules for pods (how the were used, what they could and could not do).
I've left the best till last. The language and the poetry thereof really lift this out of the commonplace. You can pick your own favourites, but I love the way writers like Bradbury, Zelazny and Simak can build concoctions of mood and image with their word mastery. Emmi Itäranta could hold her head up in such company.
It's not perfect, but it's dam' good and as my thoughts turn to candidates for the SFWA Norton (the "YA Nebula"), this is one I'll push.