Backflow Prevention Basics

About this course.

Backflow is the unwanted reversal of flow in a plumbing system, so that water travels backwards from a point of use toward the drinking-water supply instead of forward from the supply to the tap. It is dangerous because if that reversed flow passes through a point where the potable supply is connected to a source of contamination, it can pull pollutants — chemicals, wastewater, garden or industrial fluids, or micro-organisms — back into the pipes that deliver drinking water, potentially to the building's own occupants and, in the worst cases, to the wider public network. Preventing backflow is therefore fundamentally about protecting public health by keeping the potable supply one-directional and clean.

The principle at the heart of the subject is the protection of potable water. Treated drinking water is delivered to properties under pressure on the understanding that it will flow only outward to fixtures and appliances. The system is designed and maintained to keep that water free from contamination all the way to the point of use. Any pathway by which non-potable water or other substances could enter the potable pipework undermines that guarantee. Because a single property's plumbing can, under the wrong conditions, feed contamination back into the shared main, backflow is not only a private risk to one building's occupants but a potential risk to everyone downstream on the same supply. That shared exposure is why water authorities and plumbing regulators treat backflow prevention so seriously and why it is regulated rather than left to individual judgement.