Which of the following is NOT a primary function of firestop systems?

Firestop systems are specifically designed to maintain the integrity of fire-rated barriers and prevent the spread of fire and smoke within buildings. Their primary functions include restricting fire spread, controlling smoke passage, and reducing heat transfer, all of which are essential components in fire protection and safety measures mandated by building codes and standards.

The role of preventing water leakage does not fall under the primary functions of firestop systems. While maintaining a barrier against fire and smoke is critical, protecting against water infiltration is generally addressed through other methods, such as waterproofing and drainage systems. Thus, selecting "preventing water leakage" as the option that is not a primary function accurately reflects the intended purpose and capabilities of firestop systems.