Which of the following is an example of a cross-connection?

A cross-connection refers to any actual or potential connection between potable (drinking) water and non-potable water or contaminants, which can lead to the contamination of the drinking water supply. Having a hose in a mop bucket creates a scenario where the potential for backflow exists, especially if the water in the mop bucket becomes dirty or contaminated. If the pressure in the system were to drop, this could allow contaminated water from the bucket to flow back into the clean water supply. This makes it a clear example of a cross-connection.

In contrast, the other options represent systems designed to maintain a separation between potable and non-potable water. A faucet using an air gap is specifically designed to prevent backflow by creating a physical distance between the faucet and the source of potential contamination. A closed water tank typically has a sealed system that prevents contamination of the water inside. A disinfected sink would also not present a cross-connection since it is designed to handle clean water and has been treated to eliminate pathogens. Therefore, the scenario involving the hose in the mop bucket most clearly illustrates the concept of a cross-connection.