In a slow cooker, combine the onion, garlic and sausage. Stir in the beans and water and season, to taste, with salt and pepper. Cover and cook on low heat until the beans are tender, about 7 1/2 hours (on high it takes between 3 1/2 to 4 hours). Remove 1/4 cup of beans from slow cooker; mash until smooth, then sir them stir back into slow cooker. Continue to cook for another 30 minutes on low or 15 minutes on high. Remove the beans from the cooker to a serving bowl. Serve over cooked rice and enjoy!