Which term describes the contamination of the water supply because of a negative pressure condition?

The correct answer is back-siphonage, which refers specifically to the phenomenon where water is drawn back into the potable water supply due to negative pressure conditions, such as when there’s a sudden drop in pressure in the supply line. This drop in pressure can occur due to various reasons, including a large water usage event or a break in the water main. When this negative pressure occurs, it creates a vacuum that can suck contaminated water from other sources—like irrigation systems or storage tanks—back into the clean water supply, leading to potential health risks.

Backflow, while related, is a broader term that encompasses any reversal of flow in a plumbing system, which can occur both under positive and negative pressure conditions. Cross connection refers to an actual physical link between the potable water supply and a non-potable source, which can lead to backflow situations, but it does not specifically denote the negative pressure condition that causes back-siphonage. Overpressure typically refers to situations where pressure in a system exceeds normal levels, which does not directly relate to the concept of contamination resulting from a drop in pressure.