The Mercy Journals

This dystopian novel is set thirty years in the future, in the wake of a third world war waged as a result of a water crisis that ends in catastrophic destruction. When Mercy's long-lost brother Leo, arrives with news that his children have been spotted, the two brothers travel into the wilderness to look for them. What they find is that the line between truth and lies becomes indistinguishable; challenging Mercy's own moral code about the things that matter amid the wreckage of war and tragedy.

Synopsis from Open Library.