A Pressure Drop, a Plating Shop, and a Complaint About Chemical Taste

Treat this as a possible backflow incident until the data says otherwise.

Pressure at 8 psi for 2.5 hours creates backsiphonage potential at every unprotected connection in the affected area. A plating shop with boiler treatment chemicals and no containment assembly is precisely the hazard you cannot wave off, and 'nothing has changed at my building' is what every facility manager says.

Immediate actions:

• Notify the state drinking water program within 24 hours of the pressure loss event - confirm the trigger and reporting format in your state's rule, because a low-pressure event is itself reportable in many jurisdictions.
• Sample the affected taps and the main for total coliform and E. coli, and for the specific chemicals on site. Get the shop's safety data sheets before you write the analyte list; 'chemical taste' is not a lab request.
• Ask the shop directly what connections exist between process water, boiler makeup, and the potable line, and walk the building rather than accept a phone answer.
• Flush the main in both directions until residual and turbidity are normal, and consider a precautionary boil water advisory for the block while results are pending.

Free chlorine of 0.1 mg/L at the tap is not proof of contamination, but it does tell you the water has been sitting or has been diluted by an unchlorinated source.

Root cause: no containment. The plating shop service has no reduced-pressure principle assembly. 'Grandfathered' describes when it was installed, not whether it protects the main.

Immediate containment:

• Install an RPZ on the 2-inch service, verify there is no bypass, and test and tag it.
• Survey the whole park by hazard class. The car wash has hose bibs in pits and possibly reclaimed water; the restaurant has carbonators, a classic CO2 backflow path; irrigation, boiler makeup and fire sprinkler connections all need review.
• Address thermal expansion once a check valve is added. A small 2-inch service heating a closed volume can push pressure up hard enough to damage the plumbing or lift a relief valve.

Program level:

• A written cross-connection control ordinance with containment requirements tied to hazard class rather than to installation date.
• Annual testing by a certified tester, with records retained and auditable.
• A premise inspection schedule and a hazard inventory that is updated when tenants change.
• A main-break procedure that automatically triggers a sanitary survey and targeted sampling on any block where pressure fell below 20 psi.

Notification follows the result, not the complaint.

• If any sample is E. coli positive, that is a Tier 1 violation with public notice typically within 24 hours.
• If a chemical contaminant is confirmed above its MCL, the required tier and timeframe depend on the contaminant and the exposure route - confirm in the regulation rather than guessing.
• If everything comes back clean and the taste complaint traces to the repair itself, you still owe the customers an explanation and the state a closing report on the pressure-loss event and the assessment it triggered.
• A low-pressure event below 20 psi generally requires notification and a Level 2 assessment; the assessment findings, not the flushing log, are what the regulator reviews.

Do not rescind any precautionary advisory until your state's clearance protocol is met - usually two consecutive rounds of negative samples taken at least a day apart, plus a confirmed residual at the affected sites.

Close-out file: complaint times, sample times with chain of custody, flushing volumes, advisory start and end, test results, the RPZ installation and test report, and the park hazard survey. In a backflow incident, the paperwork is the defense.