The answer to 'why is my asphalt shingles water stains' is that water stains on asphalt shingles are typically caused by leaks, improper installation, or aging and deterioration of the shingles. The stains may appear as dark, discolored patches on the roof and indicate that moisture is getting through the shingles and into the underlying roof structure.
Some common causes include cracked, curled, or missing shingles, improper flashing around chimneys or vents, and buildup of moss or algae. Over time, asphalt shingles can become worn down and lose their ability to effectively shed water, leading to leaks and staining. In many cases, the stains are a sign that the roof needs repair or replacement.