Bring broth and water to a simmer in a medium saucepan; keep warm.
Heat oil in a 6-quart pressure cooker over medium heat until hot. Add onion; saute 2 minutes. Add rice and saffron; saute 30 seconds. Stir in broth mixture. Close lid securely; bring to high pressure over high heat (about 3 minutes). Adjust heat to medium or level needed to maintain high pressure; cook 3 minutes. Remove from heat; let stand 10 minutes. Place pressure cooker under cold running water. Remove lid; stir in corn, zucchini, and bell pepper. Cook, uncovered, 3 minutes; stir constantly. Stir in cheese and salt.