The answer to 'why is my skylight water stains' is that there are several common causes, including improper installation, sealant failure, or damage to the skylight itself. Water stains around a skylight are a clear sign of a leak, which can lead to further damage to your roof and home if not addressed.
The most common causes of skylight leaks include cracked or deteriorated sealant, gaps or cracks in the skylight frame, and improper installation where the skylight was not properly sealed to the roof. Over time, the sealant around a skylight can dry out, crack, and fail, allowing water to seep in. Damage to the skylight itself, such as cracks or holes, can also be a source of leaks. In some cases, the skylight may have been installed incorrectly, leaving gaps that allow water to enter.