Lentil Soup

3 T olive oil
3 medium carrots, diced
3 medium celery stalks, diced
1 large onion, diced
3 cloves garlic, minced
8 cups water
2 cups lentils
1 15-oz can tomatoes
1 t dried thyme
1 1/2 t balsamic vinegar
2 t salt

Cook carrots, celery, onion, and garlic in the olive oil until tender, about five to ten minutes. Stir in water, lentils, tomatoes, and thyme, bring to a boil, and reduce the heat. Simmer until the lentils are soft, about 30-45 minutes. Stir in the salt and vinegar, and serve.