# Backflow Preventer — Utility Construction Glossary

An assembly installed on a water service to stop non-potable water from reversing into the public supply. Common types include the reduced pressure zone (RPZ) assembly, the double check detector assembly (DCDA), and the reduced pressure detector assembly (RPDA).

## Frequently asked questions

### What is the difference between an RPZ and a DCDA?

An RPZ assembly is used where a cross-connection carries a health hazard, such as a process or makeup water line, and it discharges to atmosphere through a relief valve if either check fails. A DCDA is a double check assembly with a metered bypass, used on fire service mains so the utility can detect unauthorized use or a leak while still allowing full fire flow.

### Do backflow assemblies need annual testing?

Yes. Nearly every water authority requires backflow assemblies to be tested annually by a certified backflow tester, with results filed to the utility. A failed or untested assembly can result in the service being shut off, so testing is normally folded into a utility maintenance program.


## Related terms

- [water-main](https://www.dunninfrastructuregroup.com/glossary/water-main)
- [fire-water-loop](https://www.dunninfrastructuregroup.com/glossary/fire-water-loop)
- [zone-valve](https://www.dunninfrastructuregroup.com/glossary/zone-valve)
- [quality-control](https://www.dunninfrastructuregroup.com/glossary/quality-control)

Backflow assemblies protect the public water supply, and their annual certification is a recurring compliance obligation rather than a one-time installation item.

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Source: https://www.dunninfrastructuregroup.com/glossary/backflow-preventer
Company: Dunn Infrastructure Group — +1-912-663-1365 — contact@dunninfrastructuregroup.com
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