New York Cooling Tower Legionella Law 

Local Law 159 of 2025 significantly strengthens New York City’s cooling tower public health requirements in response to a major Legionnaires’ disease outbreak in Central Harlem in 2025. That outbreak occurred despite prior quarterly testing rules, prompting the City Council and DOHMH to conclude that more frequent monitoring was necessary to detect Legionella earlier and prevent future clusters. NYC doubles Legionnaires' inspectors, triples testing frequency ahead of summer

The law updates NYC’s cooling tower framework (originally created after the 2015 South Bronx outbreak) and is implemented through amendments to Chapter 8 of Title 24 of the NYC Health Code, adopted by DOHMH in April 2026 and effective May 7–8, 2026.

 

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Download New York Cooling Tower Legionella Law info sheet:

Key Change: Monthly Legionella Testing

The most important change is the increase in Legionella testing frequency:

  • Before: Cooling towers had to be tested at least once every 90 days while in operation.

  • Now (under Local Law 159):

    • Cooling towers must be tested at least once every 31 days (monthly) during their operating season.

    • DOHMH rules clarify that no more than 31 days may pass between samples.

This effectively increases Legionella testing from 4 tests per year to as many as 12 per year for towers that operate year‑round.

Who Must Comply

The law applies broadly to all buildings in New York City that operate cooling towers, including:

  • Commercial office buildings

  • Large residential buildings and co‑ops

  • Hotels

  • Hospitals and healthcare facilities

  • Industrial buildings with evaporative cooling systems

These requirements are specific to NYC and are stricter than New York State regulations, which still generally require quarterly testing outside the five boroughs.

 

 

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Additional DOHMH Rule Clarifications and Monitoring Requirements

Local Law 159 does not replace prior rules—it adds to them. Under the updated DOHMH regulations:

  • Seasonal startup testing (within 14 days of bringing a tower online) is still required.

  • Weekly water quality monitoring (e.g., disinfectant levels, pH, conductivity) remains mandatory.

  • Quarterly compliance inspections by qualified professionals are still required.

  • Annual certification of compliance must still be filed with DOHMH by November 1 each year

The updated rules reinforce expectations for documentation, record retention, and rapid corrective action when Legionella results exceed action thresholds.

Enhanced Warm Weather Controls

The law and accompanying rules also emphasize preventive measures during high-risk summer months:

  • DOHMH requires or expect enhanced disinfection (e.g., hyper halogenation) during periods of elevated Legionella risk, typically July 1 through August 31.

  • These measures are designed to address conditions when warm temperatures accelerate bacterial growth in cooling towers.

  • Monthly testing allows earlier identification of Legionella growth.

  • Faster detection supports quicker corrective action and outbreak prevention.

  • DOHMH has also expanded inspection capacity and reporting oversight following the 2025 outbreak.

 

Enforcement and Public Health Rationale

NYC health officials describe the law as a shift toward shortening detection windows and faster intervention:

Failure to comply can lead to violations, doubled monetary penalties, and potential shutdown orders, particularly if towers are linked to disease investigations.

Summary

Local Law 159 of 2025 fundamentally shifts NYC’s approach to cooling tower safety by moving from quarterly to monthly Legionella testing, reinforced by stricter DOHMH monitoring and documentation rules. The intent is clear: detect problems sooner, intervene faster, and reduce the risk of deadly Legionnaires’ disease outbreaks in dense urban environments.

How Pace® Supports Compliance with Local Law 159
Pace® environmental testing and analytical services are designed to support full compliance with Local Law 159 of 2025 and the updated NYC Department of Health (DOHMH) cooling‑tower requirements. As a New York State ELAP‑accredited laboratory, Pace® provides Legionella testing that meets the City’s requirements for certified laboratory analysis, supporting the mandated monthly (31‑day) sampling schedule during cooling‑tower operation.