Which term refers to an instance of unwanted water entering a system?

The correct term that refers to an instance of unwanted water entering a system is "Wassereinbruch." This term is commonly used in various technical contexts, such as construction, engineering, and environmental science, to describe situations where water inadvertently infiltrates an area or system that it should not enter. This can happen, for example, in the context of basements, tunnels, or piping systems where water may compromise structural integrity or functionality.

The other terms listed do not pertain to unwanted water intrusion. "Verdrehung" refers to twisting, "Drehmoment" relates to torque or moment of rotation, and "Entlüften" means venting or releasing air. Each of these terms has specific applications in technical and engineering fields that are entirely different from the concept of unwanted water entering a system.