Which symptom may indicate a failing water pump?

A failing water pump can lead to an overheating engine because its primary function is to circulate coolant throughout the engine and the radiator. When the water pump is not working properly, the flow of coolant is disrupted, which prevents the engine from maintaining an optimal operating temperature. As the engine heats up beyond the normal range, it can cause serious damage over time, such as warped cylinder heads or a blown head gasket.

Increased fuel efficiency, worn tires, and fluctuating battery levels do not have a direct correlation with the water pump's function. While they may indicate issues in other systems or components of a vehicle, they are not symptoms that would typically suggest a problem with the water pump. Increased fuel efficiency generally indicates that the engine is operating optimally, worn tires relate more to road contact and alignment, and fluctuating battery levels usually point to electrical system issues. Therefore, the symptom that most closely indicates a failing water pump is indeed an overheating engine.