Stir in broth, salt, and water. Bring to a boil over high heat. Stir in pasta and cook, uncovered, over medium-high heat for 2 minutes. Add zucchini, cover, and cook for 3 minutes. Uncover and continue cooking, stirring frequently, until pasta is just short of tender. (It usually takes less time than indicated on package.) If mixture becomes thick before pasta is ready, turn off heat, cover, and let sit until pasta is tender but still firm, usually no more than 2-3 minutes.