I’m gonna say probably your regulator on your outside gas meter. The cold water on the inlet never touches the burner system and shouldn’t affect it. Same with the cold air. Condensation shouldn’t be an issue after replacing all the parts at the first of the year and not having the issue before then. I’m not a gas technician so no clue on putting a gauge on the system near the WH. Some appliances (especially new ones) are more sensitive to gas pressure. You may be able to contact your gas utilities and ask them to check it for you since it is their meter and regulator (unless your on propane).