<cite index="22-1,22-2">National City's predominantly older housing stock means aging plumbing is widespread, with galvanized pipes from the 1950s and 1960s, corroding copper from the 1970s, and outdated water heaters common finds.</cite> <cite index="23-3,23-4">Hard water causes scale buildup inside tank water heaters, decreasing efficiency and shortening lifespan.</cite> <cite index="27-4,27-5">Coastal proximity to San Diego Bay means higher ambient moisture and salt content in the air, accelerating corrosion.</cite>