“Rising temperatures, longer heat waves, and high humidity for longer periods of the year are creating conditions that can increase the risk of Legionella bacteria growth in cooling towers.” This is according to a recent press release from New York City Mayor Zohran Mamdani’s office, announcing new measures from the New York City Department of Health and Mental Hygiene (DOHMH) following a Legionnaire’s disease cluster in the Upper East Side that resulted in 94 cases and 11 deaths during the summer of 2026. Not long after the announcement, another disease cluster plagued the South Bronx, resulting in 24 cases and two deaths.

Legionella bacteria occur naturally in freshwater lakes and streams but can pose a health risk in human-made water systems, particularly where organic deposits, metals, stagnant water, and warm temperatures can encourage bacterial growth. The exposure pathway is through inhalation of contaminated water vapor, emitted from building cooling towers into the surrounding ambient air or from buildings’ potable water systems through showers, sinks, fountains, hot tubs, and the like. The bacteria are known to cause a mild respiratory illness called Pontiac fever or a severe pneumonia called Legionnaire’s disease. Infection is often treatable if symptoms are identified and addressed early.

With cooling towers at the center of recent outbreaks, New York State has enhanced maintenance and compliance requirements. In August 2026, Governor Kathy Hochul signed into law an amendment to the New York City Administrative Code, which now requires cooling tower owners or operators to file biannual certifications regarding inspection, testing, cleaning, and disinfection in January and July of each year or by dates specified by the New York City Department of Buildings (NYC DOB). The amendment also increases retention of test results from three years to ten years, and more significantly, increases civil penalties for violations to $2,500 for a first violation, $7,000 for a subsequent violation, and up to $12,500 for a violation that results in a fatality or serious injury.

This is in addition to New York City’s Local Law 159 (codified at Admin. Code § 17-194.1) and DOHMH regulations that went into effect in May 2026, which require building owners to test cooling towers for Legionella every 31 days when the cooling tower is operating, require testing by a laboratory certified by the New York State Environmental Laboratory Accreditation Program (ELAP), prescribe tightened timelines for notification and remediation, require notification for shutdown and startup, and increase penalties by twofold.

In addition, as the Mayor announced in September 2026, DOHMH will cooperate with NYC DOB to identify unregistered cooling systems, enhance mapping features on its cooling tower lookup tools, and accelerate enforcement of cooling tower violations by endeavoring to assign a hearing date within 15 days after the service of summons. DOHMH will also convene a scientific advisory panel to explore and evaluate new and alternative technologies to reduce reliance on cooling towers.

Meanwhile, New Jersey’s Legionella water management requirements adopted through Senate Bill S2188 (codified at P.L. 2024, c. 66) are now in effect. September 12, 2026 was the deadline for owners and operators of certain buildings (including without limitation hospitals, nursing homes, long-term care facilities, residential high-rise structures with six or more floors with centralized potable water-heater systems, hotels and motels with a centralized water heating system shared by 25 or more units, and certain senior and disability housing buildings) to establish water management programs consistent with ASHRAE Standard 188-2018 to minimize the growth and transmission of Legionella. Owners and operators of buildings with certain features such as a whirlpool, spa, pool, cooling tower, atomizer, humidifier, and certain other devices that release water aerosols in the building or on the property are also required to comply on a device-specific level. December 12, 2026 is the deadline for building owners and operators to fully implement their water management programs. The NJ Department of Health may assess penalties of up to $2,000 for a first violation, $5,000 for a subsequent violation, and $10,000 for a violation that causes serious injury or death.

SPR is tracking the Legionella compliance developments in New York and New Jersey as part of its Environmental Issues in Real Estate Management practice.