Slow Cooker Three-Bean & Barley Soup

Source: Eating Well (slightly modified by Aimee)

2 cups water
4 cups (32-ounce carton) vegetable broth
1/2 cup pearl barley
1/3 cup dried black beans
1/3 cup dried great northern beans
1/3 cup dried kidney beans
1/2 cup corn kernels
1 tablespoon chili powder
1 teaspoon ground cumin
1 teaspoon dried oregano
1 teaspoon salt (plus extra to taste)
pepper to taste
1 tablespoon extra-virgin olive oil
1/2 cup diced onion
1 large stalk celery, diced
1 large carrot, diced
2 cloves garlic, chopped

1. Soak beans overnight; drain & rinse.
2. In slow cooker, place water, broth, barley, black beans, great northern beans, kidney beans, corn, chili powder, cumin, oregano, & salt.
2. Heat oil in skillet. Add onion, celery, carrot, & garlic and cook, stirring occasionally, until softened, about 5 minutes. Add to slow cooker.
3. Cover & cook on high 4 hours; reduce to low and cook at least 2 hours more. Season with salt & pepper.