Preheat a medium-sized stock pot over medium-high heat. Add butter, onion and garlic, and cook until softened, stirring frequently, about 4 minutes. Sprinkle flour over the mixture and stir to combine. Add water and chicken broth and continue to stir until it boils. Turn the heat to low and add salt and pepper to taste. Add the remaining vegetables and stir. Stir in the chicken and fresh herbs. Continue to cook soup until vegetables are crisp-tender. Stir in the tortilla squares. Taste and adjust seasoning with salt and pepper. Serve warm.