Not a Drop to Drink by Mindy McGinnis
Synopsis from GoodReads:
Regret was for people with nothing to defend, people who had no water.
Lynn knows every threat to her pond: drought, a snowless winter, coyotes, and, most importantly, people looking for a drink. She makes sure anyone who comes near the pond leaves thirsty, or doesn’t leave at all.
Confident in her own abilities, Lynn has no use for the world beyond the nearby fields and forest. Having a life means dedicating it to survival, and the constant work of gathering wood and water. Having a pond requires the fortitude to protect it, something Mother taught her well during their quiet hours on the rooftop, rifles in hand.
But wisps of smoke on the horizon mean one thing: strangers. The mysterious footprints by the pond, nighttime threats, and gunshots make it all too clear Lynn has exactly what they want, and they won’t stop until they get it….