The answer to 'why is my air duct water damage' is that there are several common causes, including leaks in the HVAC system, condensation buildup, and flooding. Symptoms can include visible water stains, musty odors, and mold growth. Solutions may involve repairing leaks, improving insulation, or replacing damaged ductwork.
If the water damage is extensive or you suspect mold growth, it's best to call a professional air duct cleaning service. They have the equipment and expertise to properly assess the issue, clean and disinfect the ducts, and make any necessary repairs. Attempting to DIY air duct cleaning with water can actually make the problem worse by spreading mold and bacteria throughout your home.