New York City has regulated cooling towers since Local Law 77 of 2015, passed after that year's Legionnaires' disease outbreak in the South Bronx. In 2025 the City Council passed Local Law 159, which moved Legionella culture testing from at least every 90 days to at least every month while a tower operates. The Health Department's amended rules, 24 RCNY Chapter 8, took effect in May 2026. This guide summarizes what they require. It is a summary, not legal advice: the rule text is linked below and governs.
Legionella testing: monthly, by an ELAP lab
- Frequency. Legionella culture testing at least as often as every month, with no more than 31 days between samples, while the cooling tower system is operating (§8-05(f)(3)). The Department dropped the word "calendar" from "month" specifically to make the 31-day spacing the rule.
- Laboratory. Samples must be analyzed by a laboratory accredited by the New York State Environmental Laboratory Approval Program (ELAP). The final report must include a copy of the signed chain of custody and the lab's ELAP certification number.
- Reporting. Owners report the date of each Legionella sample to the Department within 5 days (from Local Law 76 of 2019). Results at level 4, 1,000 CFU/ml or more, must be reported within 24 hours of receiving them.
What a result requires (Table 8-1)
| Level | Legionella | Required response (summary) |
|---|---|---|
| 1 | < 10 CFU/ml | Maintain chemistry and biocide; if detected, review and adjust the program |
| 2 | 10 to < 100 | Disinfect within 24 hours; review treatment; retest in 3–7 days |
| 3 | 100 to < 1,000 | As level 2, plus visual inspection for cleaning; retest in 3–7 days |
| 4 | ≥ 1,000 | Disinfect within 24 hours; full remediation within 48 hours (hyperhalogenate, drain, clean, flush); notify the Department within 24 hours; retest in 3–7 days |
Emergency sampling triggers
Additional Legionella sampling is required after events such as a power failure long enough to allow bacterial growth, a loss of biocide treatment, or a failure of conductivity controls to maintain proper cycles of concentration. In NYC, cycles control is part of Legionella control.
Other routine obligations
- Weekly bacteriological indicator. A bacteriological indicator at least once a week while the tower operates. If it is done by heterotrophic plate count (HPC), an ELAP-accredited lab must analyze it. Dip slides, read outside a lab, are still allowed.
- Maintenance program and plan (MPP). A written plan following ASHRAE 188, developed by a qualified person and now certified annually by one. The MPP must include a valve schedule.
- Qualified person means a New York State licensed professional engineer, a certified industrial hygienist, a certified water technologist with ASHRAE 188 experience, or an environmental consultant with at least two years of water-management experience.
- Records of maintenance, inspections, test results and corrective actions must be kept for at least 3 years.
- Automated monitoring is permitted for the routine process-control measurements if the MPP shows how those measurements are monitored.
Penalties
The amended penalty schedule raises many first-violation amounts. For example, failing to produce the annual plan certification is $2,000 for a first violation and $4,000 for a repeat. Routine monitoring not conducted or documented at least weekly while the tower is in use is $1,000 and $2,000.
What this means in practice
Monthly testing mostly adds lab and technician visits, and many owners rely on their water-treatment company to take samples and file the dates. The harder part is keeping the operating data (conductivity and cycles, biocide residuals, startup and shutdown dates, corrective actions) complete and consistent enough to prove control, and seeing early when the water side starts to drift. That operating record is also where water savings and chiller efficiency live: see cycles of concentration and condenser approach and fouling.