Which of the following can indicate a potential issue with a roof's drainage system?

Pooling water on the surface of a roof after heavy rain is a clear indicator of potential issues with the roof's drainage system. This phenomenon suggests that the roof may not be sloped properly or that there are blockages in the gutters or drains that prevent water from flowing off the roof effectively. Water pooling not only indicates inadequate drainage but can also lead to other problems such as leaks, roof degradation, or structural damage over time as water accumulates and seeps into the roofing materials. Monitoring for pooling water is crucial for the maintenance and longevity of the roof, making this answer particularly relevant when assessing drainage issues.

While uneven color of roofing material, leaves on the roof, and rusting nails can signal potential maintenance issues, they do not directly relate to the drainage system's effectiveness.