The answer to 'why is my fascia water stains' is that the fascia, which is the board that runs along the edge of your roof, is likely experiencing water damage due to a leak or improper drainage. This can be caused by issues like clogged gutters, damaged roof shingles, or poor installation of the fascia itself.
Some common symptoms of water-damaged fascia include visible stains, warping, or even rotting of the wood. If left untreated, this can lead to further damage to your roof and home's exterior. To address the problem, you'll need to identify and fix the root cause, such as clearing debris from gutters, repairing roof leaks, or replacing the fascia boards if they are severely deteriorated.