What does the code define as the flow of liquids into the distributing piles of a potable water system from an unintended source?

Backflow is defined as the flow of liquids into the distributing pipes of a potable water system from an unintended source. This phenomenon can occur when there is a difference in pressure that causes contaminated water to flow in the reverse direction, potentially leading to serious health risks due to the mixing of potable water with non-potable sources.

Understanding backflow is crucial for plumbing professionals, as it helps in preventing contamination of drinking water supplies. Measures such as backflow preventers are typically installed in plumbing systems to mitigate this risk, ensuring that the integrity of the potable water supply is maintained and safeguarded against impurities that could arise from cross-connections with other systems or sources.

The other choices, while related to water systems, do not accurately describe the specific scenario of unintended flow into potable water systems. For example, cross-connection refers to the physical connection between potable water and a non-potable source, which can lead to backflow but is not the description of the flow itself. Contamination refers to the presence of harmful substances or pollutants in water, while leakage pertains to the unintentional escape of water from pipes or fixtures, neither of which specifically address the flow reversal that backflow describes.