Backflow prevention device

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A backflow prevention device is used to protect water supplies from contamination. Many types of backflow devices also have ports so that they can be tested or examined to ensure that they are functioning properly. A check valve is a common form of backflow preventer.

Backflow prevention protects the potable water system from from minor, moderate, and severe hazards. There are over 10,000 reported cases of backflow contamination each year. Some cases can be fatal. Backflow devices are required by law where needed and must be installed in accordance with plumbing code. A backflow assembly has test cocks and shut-off valves and must be tested each year, if relocated or repaired, and when installed.

In this situation, dirty water from the hillside pool will back siphon or back flow down the hosepipe and into the clean water tank. To prevent this from happening, the house's external tap should be fitted with a backflow prevention device.

[edit] Partial list of some backflow prevention devices

Air gap
Atmospheric vacuum breaker (AVB)
Chemigation valve (primarily used in agriculture)
Check valve
Double check valve, or double check valve assembly (DCVA)
Pressure vacuum breaker assembly (PVB)
Reduced Pressure Backflow Prevention Assembly (RP), or reduced pressure principle assembly
Reduced pressure zone device (RPZ)