I would have given this book 3.5 stars, were that possible. I loved the characters and the technical language of water reclamation. I thought the central metaphor of the slow river of the title worked well, covering the literal water work the protagonist does, the symbolic currents of history, and a river's potential to cleanse or drown.
That said, I was unclear about when and where this novel was set. It's a dystopian future with slides for transport and identity implants, but people also watch TV, plant seeds in actual dirt, and drink beer. I would have liked more terraforming and less sex, but that's probably just the old Trekkie in me.