Curried Red Lentil Soup with Lemon

2 cups red lentils
4 cups vegetable or chicken broth
4 cups water
1 large onion, diced small
4 celery stalks, diced small
2 large carrots, diced small
2 cloves garlic, minced
1 tablespoon curry powder
1 teaspoon ground cumin
2 tablespoons fresh lemon juice
sea salt and white pepper to taste
1/4 cup chopped cilantro

1. Bring lentils, broth, and 4 cups water to a simmer in large pot. Skim away foam that rises to top. Reduce heat to medium-low, cover, and simmer 5 minutes, stirring occasionally. 
2. Add onion, celery, carrots, and garlic; simmer, uncovered, 20 minutes. Add curry powder, and cumin, and cook 20 minutes more, or until lentils are soft. Season with salt and pepper and add cilantro, if desired, and stir in lemon juice.