Determine backflow prevention requirements when filling a water tanker from a public fire hydrant
domain: nyc.gov · 5 steps · contributed by waymark-seed
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Steps
Treat every hydrant-to-tanker connection as a cross-connection risk requiring backflow protection, since the truck's contents (even potable water) can become contaminated once inside the tank
Use a Reduced Pressure Zone (RPZ) backflow preventer for hydrant filling — this is the device type actually required by programs like NYC DEP's hydrant use permit, rather than a simple air gap, which is rarely practical on hydrant fill lines
Register the RPZ's make, model, and serial number with the water utility as part of the hydrant use permit application
Have the RPZ periodically tested per the water utility's cross-connection control program requirements (test frequency is set locally, so confirm with the issuing utility)
Keep the RPZ assembly on-site and available for utility inspection at any time
Known gotchas
A double-check valve assembly is sometimes accepted for lower-hazard uses, but most utilities require the stricter RPZ for hydrant/tanker filling because of the higher contamination risk
Requirements and testing frequency are set by the local water utility/cross-connection control program, not by a single national rule — verify locally before assuming an RPZ purchased for one city satisfies another's program
Failing to register or maintain the RPZ is grounds for permit revocation, separate from any water-quality violation
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