Local Law 159: NYC Cooling Towers Now Require Monthly Legionella Testing

Under existing rules, cooling tower owners were required to test for Legionella bacteria every 90 days during the operating season. Under Local Law 159:

• Testing is now required monthly for all operating cooling towers
• Minimum samples per season increase significantly — from roughly 3–4 to 9–10 per full season
• Year-round cooling tower operators face even higher testing frequency
• All testing must still be conducted by a state-certified laboratory

The law was passed by the City Council in October 2025 and becomes enforceable starting May 7, 2026 — just ahead of the start of NYC's primary cooling season.

Legionella bacteria thrive in warm water systems — including cooling towers — and can cause Legionnaires' disease, a serious and sometimes fatal form of pneumonia. NYC has been a national leader in cooling tower regulation since a major Legionnaires' outbreak in the South Bronx in 2015 killed 12 people and infected over 120.

DOHMH proposed new rules in early 2026 to further tighten maintenance standards, including new requirements around chemical treatment evaluation and startup procedures. Monthly testing is the most immediate operational change owners must prepare for.

Separate from monthly testing, Local Law 159 and associated DOHMH rules also update the seasonal startup and shutdown process:

• Before startup: Clean and disinfect the cooling tower within 15 days before operation
• After any shutdown: Notify DOHMH electronically within 5 days
• After any startup: Notify DOHMH electronically within 5 days
• After extended inactivity (5+ days of no circulation): Clean and disinfect before resuming operation

These notification requirements are enforced through the NYC Cooling Tower Registry, which all cooling tower owners are already required to use.

The updated DOHMH rules also introduce stricter standards for chemical treatment programs:

• Before changing an existing chemical treatment system, a qualified person must evaluate compatibility and minimize microbial growth risk
• That evaluation must document the optimum treatment levels for the specific system
• Changes to cooling tower design, installation, or operation that affect water treatment must also be evaluated

This means ad-hoc chemical changes — switching vendors or products mid-season without a documented evaluation — are no longer acceptable under the new rules.

• Contact your cooling tower vendor now to update your service contract to include monthly Legionella sampling
• Confirm your laboratory is state-certified and can accommodate monthly scheduling
• Update your maintenance program and plan to reflect the new sampling frequency — this document must be kept on-site and available for DOHMH inspection
• Schedule seasonal startup and build in the required cleaning and disinfection window 15 days before you plan to run the system
• Verify your NYC Cooling Tower Registry registration is current — newly installed towers must also be registered with DOB

Monthly testing will increase operating costs for covered buildings. According to Tower Water, the shift from quarterly to monthly testing can more than double annual Legionella testing expenses depending on system size and lab fees. Building owners should factor this into 2026 operating budgets now rather than absorbing it mid-season.

DOHMH has authority to issue fines and violations for cooling tower non-compliance under Section 17-194.1 of the NYC Administrative Code. Non-compliant buildings can also face:

• Required emergency cleaning and disinfection at the owner's expense
• Mandatory shutdown orders
• Public reporting of violation status