A leaking check valve may be caused by which of the following?

A leaking check valve can indeed often be attributed to a dirty or damaged check disc. The check disc is a critical component that needs to form a tight seal to prevent backflow. When the check disc becomes dirty or damaged, it cannot close properly, allowing water to leak through the valve instead of blocking reverse flow as intended. This situation compromises the valve's function, which is to protect the potable water supply from contamination.

While excessive water pressure and incorrect installation may lead to other issues with plumbing systems, they are less directly related to the specific consequences of a leaking check valve compared to the condition of the check disc itself. A dirty or damaged disc is a more common and direct cause of leakage in check valves, making it the most accurate choice in this context.