What is a check valve mainly used for in a water system?

A check valve is primarily utilized in water systems to ensure that water flows in one direction and to prevent backflow. This is particularly important in various applications, such as preventing contamination of clean water sources by stopping water that may flow back into the well casing, which could occur due to pressure changes or other factors. The effective operation of check valves helps maintain system integrity by ensuring that the water distribution process is efficient and safe.

In this context, the correct option emphasizes the critical role of check valves in maintaining the direction of flow within a system, thereby protecting both the water quality and the components of the water system. Other options address different functionalities that are not related to the primary function of check valves, such as backup sources of water, measuring water levels, or supporting motor bases, which do not describe the essential role of a check valve.