1Heat oil in a Dutch oven over medium heat. Add onion, celery and carrot and cook, stirring occasionally, until softened, about 5 minutes. Add water, broth, barley, black beans, great northern beans, kidney beans, chili powder, cumin and oregano. Bring to a lively simmer over high heat. Reduce heat to maintain a simmer and cook, stirring occasionally, until the beans are tender, 1¾ to 2½ hours (adding more water, ½ cup at a time, if necessary or desired). Season with salt.
2Slow-Cooker Variation: Use 2 cups water (instead of 9 cups) and combine all ingredients in a 5- to 6-quart slow cooker. Cover and cook until the beans are tender, about 4 hours on High or 7 to 8 hours on Low.
Make Ahead Tip: Cover and refrigerate for up to 3 days.
For easy cleanup, try a slow-cooker liner. These heat-resistant, disposable liners fit neatly inside the insert and help prevent food from sticking to the bottom and sides of your slow cooker.