Water is supposed to flow one way. When it flows backwards, or when a clean supply is joined to a dirty one, contamination can be pulled into the main. The assessment checks you understand how that happens and how it is prevented.
What backflow and cross-connection covers in the assessment
- Backflow is water flowing the wrong way back into the clean supply, carrying contamination with it
- Back-siphonage is backflow caused by a drop or loss of pressure in the main, such as a burst or heavy demand
- A cross-connection is any unintended link between potable water and a non-potable source
- Leaving a hose submerged in a tank, pond or puddle is a classic cross-connection risk
- Backflow is prevented by air gaps and by check valves (single or double) chosen for the level of risk
- A standpipe drawing from a hydrant must have a double check valve
Where people slip up
Leaving a hose end under water. If pressure drops it can be siphoned back into the main.
Thinking backflow only matters at high pressure. A loss of pressure is what causes back-siphonage.
Using a standpipe with no backflow protection. A double check valve is required.
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