Heat a cast-iron pot over medium-high heat. Add the bacon and cook for 5 minutes. Add the onion and saute until beginning to soften and become translucent, about 5 minutes. Add the garlic and saute until fragrant, about 1 minute. Season with salt and pepper. Add the beans and 5 cups water to the pot, stirring to combine. Bring the beans to a boil, reduce the heat and cover. Cook over medium-low heat until the beans are tender, about 2 hours. Adjust the seasoning, if necessary.