Have you checked the flue?

Be sure to check your gas water heater (and furnace) exhaust flue to ensure it is properly sloped to prevent water from accumulating. If water pools within the flue, it can lead to rust and eventually cause leaks, potentially damaging the unit, floors, or ceilings. In the attached photo, you can see an example of improper slope, allowing water to collect inside the flue. Fortunately, H&H identified this issue during a routine inspection.