Which device can help prevent air from entering the water stream when packing does not provide an effective seal?

The correct choice is lantern rings because they are specifically designed to prevent air from entering the water stream in situations where a standard packing may not form a sufficient seal. Lantern rings are components used in valve and pump assemblies, located within the packing area around the shaft. They provide a space that helps in the retention of lubrication while also preventing air from infiltrating the system.

By ensuring a tighter seal and reducing the possibility of air leakage, lantern rings enhance the efficiency of the water distribution system. This is particularly important in maintaining proper pressure and flow within the system.

While sealing tape, ball valves, and check valves serve important functions in a water distribution system, they do not primarily serve the purpose of preventing air from entering the water stream in the same way that lantern rings do. Sealing tape is typically used to create seals on threaded connections, but it does not address air infiltration effectively. Ball valves control the flow of water but do not provide a mechanism to prevent air from entering. Check valves prevent backflow but are not intended to function in sealing applications where air may enter. Thus, lantern rings are the most appropriate choice for the specific function described in the question.