Place a Dutch oven or stockpot over medium heat. Add butter to the Dutch oven. When butter has melted stir in onions and carrots. Cook for about 5 minutes or until soft. Stir in broccoli, broth, water, and salt.
Or, remove about 1 cup of soup and puree in a blender, with the center part of the blender lid to allow steam to escape. Run blender with a clean towel over the lid. Return blended soup to the Dutch oven. Repeat if you prefer.