What waterproof rating do I actually need for a shower speaker?

IPX7 or IP67 is the practical floor. Both ratings cover full submersion in up to 1 meter of water for 30 minutes, which is more than enough for steam, direct spray, and the occasional drop in the tub. IPX4 'splash-resistant' speakers can survive a shower but aren't engineered for it; reviewers consistently recommend IPX7/IP67 for bathroom use.