Set a large soup pot over medium-high heat, add olive oil. Let heat for 30 seconds and add onion. Season with 1/4 teaspoon salt and cook for 2 minutes, stirring occasionally. Add garlic, mushrooms, carrots, celery, mushrooms and rosemary and cook for another 3 minutes, stirring occasionally. Add vegetable broth and water, cover pot, and cook for 15 minutes.