Final answer:
A plumbing cross-connection is a potentially hazardous situation where the drinking water supply is linked to a source of contamination, and it could introduce pollutants into the water system. Air-filled tubes near faucets, called air gaps, prevent this by ensuring there's no direct connection that could allow backflow of contaminants.
Step-by-step explanation:
A plumbing cross-connection is a situation where the potable water supply is directly connected to a source of contamination or pollution. This could lead to contaminants entering the drinking water system, posing a serious health risk. In a proper plumbing system, measures are taken to prevent cross-connections, such as the inclusion of air-filled tubes, or backflow preventers.
Air-filled tubes, often found near water faucets, are known as air gaps and serve as a simple but effective backflow prevention method. They are needed to ensure that, in the event of a sudden drop in water pressure, contaminated water from sinks or fixtures doesn’t get siphoned back into the clean water supply. These air gaps work by maintaining a physical separation between the outlet end of the faucet and any potential source of contamination, effectively preventing direct connection and thereby protecting the potable water system.