Thirst by Iris Sweetwater

Left for dead by her own flesh and blood, Brenna will have to learn to fight to stay alive in this post-apocalyptic world . . .
Brenna has been known for breaking the rules of her underground colony most of her life, but now that she is of age, the stakes are much higher. Banishment from her colony means more than just losing her family ties. Since humans all but destroyed it, the world has been a harsh place with little food or shelter and no safety from the worst human beings imaginable.
Brenna’s life is saved by a tribe who has learned to live on the surface, and with them she will thrive.
But what happens when the ambitions and prejudices of those below endanger this new family she has found? Brenna feels she has no choice but to go on a dangerous trek in search of a rumored utopia where they might all find peace.
But peace always comes at a price.