What is characterized as backpressure?

Backpressure is defined as a condition where the pressure in the system exceeds the pressure of the water supply. This situation can occur in various scenarios, such as when a pump or other source generates pressure in a system that pushes fluids back into the potable water supply.

Understanding backpressure is crucial because it poses a risk of contamination if not properly controlled, especially in systems where non-potable water is used. For example, if a downstream system has higher pressure due to a pump or changes in elevation, it could force contaminants from the plumbing system back into the drinking water supply unless appropriate backflow prevention devices are in place.

The other conditions listed don't represent backpressure. Pressure below the supply pressure or equal to it would not create any risk of backflow, and a zero pressure condition indicates no flow or pressure in the system, which further does not relate to the concept of backpressure.