Which scenario is considered a common cross connection?

A common cross connection is a situation where a potable water supply is connected to a non-potable source, creating a risk that contaminants can enter the public water supply. In scenario C, the chemical container linked to potable water exemplifies this situation because it poses a risk of chemicals entering the drinking water system. If there is a backflow event, toxic substances from the chemical container can contaminate the potable water supply, which poses serious health risks to consumers.

In contrast, while the other scenarios might present risks in their own right, they do not illustrate the classic definition of a cross connection as clearly. For example, a garden hose connected to city water does not directly create a risk unless it is used improperly, such as submerged in a contaminated source. A fire hydrant connected to a private well raises concerns about well water quality but doesn't fit the traditional definition of a cross connection affecting the public supply. Similarly, a storm drain connected to sewer lines deals with storm water management issues rather than directly connecting potable water supplies to contaminants. Thus, the key element of a cross connection, reflected in scenario C, is the direct potential for contamination of drinking water through improper connections.