After the Storm: Why Extreme Rainfall Should Trigger a Cooling-Tower Legionella Protocol

Chantil Cammack
Aug 26
2 min read

This summer’s Central Harlem Legionnaires’ cluster is a wake-up call for every facility with cooling towers. New York City health officials report over 100 cases and multiple deaths, and confirmed 12 cooling towers tested culture-positive for Legionella across 10 buildings. That’s not just a New York problem it’s a pattern we see whenever heat and heavy rainfall collide.

Why storms raise your risk:

Heat, humidity, and intense downpours create conditions cooling systems struggle with: temperature swings, dilution of biocide residuals, organic load, and operational upsets. Climate-driven extremes are expanding where and when outbreaks happen, not just in NYC but across the broader U.S. as well.

What regulators and standards expect:

If you’re accredited or survey-facing, your Water Management Program should already outline how you control Legionella, but many plans don’t include severe-weather triggers. Align your WMP with:

Legionellosis risk management for building water systems
Risk management to physical, chemical, and microbial hazards encouraging a more systematic, lifecycle approach

Your 10-step Post-Storm Cooling-Tower Protocol

Trigger & timing: Start this protocol whenever your area experiences heavy rainfall, flooding, or stormwater intrusion OR when makeup water quality deviates from baseline.
Immediate system check: Verify tower basins, drift eliminators, louvers, and overflow/return paths for debris or stormwater ingress. Document findings in your WMP log.
Measure & record key parameters: Record temperature, pH, conductivity, ORP/oxidant residual, and turbidity at makeup and basin. Compare to site-specific control limits.
Restore disinfectant control: If residuals are below your control limits, follow your pre-approved WMP control response to restore them promptly (per your chemicals and local regulations). Avoid ad-hoc dosing, follow the written plan.
Blowdown & purge: Increase blowdown/bleed-off if stormwater has diluted the system. Resume normal setpoints once parameters stabilize.
Physical cleaning: Remove debris and organic matter from the basin and strainers; check side-stream filtration and separators. Biofilm + nutrients = Legionella fuel.
Enhanced monitoring window (48–72 hours)Run accelerated checks (e.g., daily oxidant residuals/ORP; ATP or heterotrophic plate count if used on site). If any indicator drifts toward corrective thresholds, escalate per WMP.
Targeted Legionella testing: Where your risk matrix calls for it (e.g., hospitals, LTC, or after any control excursion), collect post-event Legionella samples. Use an accredited lab and tie results to pre-defined actions.
Verification & validation: Log all readings, actions, and outcomes in your CRM/WMP dashboard. Confirm setpoints are back in range and close the event with a short summary.
Lessons learned: Within 7 days, review trends: Did residuals crash? Did organic load spike? Update your setpoints, sampling locations, or trigger thresholds accordingly.

Where Legionella Specialties fits in

Rapid post-storm assessment & sampling: On-site checks, targeted Legionella testing, and lab logistics.
Program tuning: We can update your R3 Report and ASHRAE-aligned WMP with a severe-weather appendix and dashboard triggers.
Ongoing protection: AquaGuard MO (mineral oxychloride) treatment programs and continuous monitoring to keep residuals stable and biofilm pressure low between events.
Survey-ready documentation: Our CRM captures setpoints, alarms, actions, and results to support Joint Commission and health-department reviews.

Bottom line

Storms are now a reliability test for your cooling-tower controls. A written, rehearsed Post-Storm Protocol closes the gap between what standards expect and what actually happens the morning after a downpour. If Harlem taught us anything this summer, it’s that preparation beats crisis response every time.