Understanding Cooling Tower Local Law 159 of 2025

If you own or manage a commercial building in New York City with a cooling tower, evaporative condenser, or fluid cooler on a recirculated water system, the rules governing how you maintain it just changed. Local Law 159 of 2025 amends the cooling tower requirements that have been in place since 2015, and it adds real obligations you will want to plan for now rather than scramble to meet later.

The original law came out of the 2015 Legionnaires' disease outbreak in the Bronx. It required owners to register their cooling towers with the Department of Buildings, keep a written maintenance program built around ASHRAE Standard 188-2015 and the manufacturer's instructions, and have the equipment inspected and tested at least every three months while in use. It also set an annual certification due each November 1, a three-year recordkeeping rule, and civil penalties for owners who fell out of compliance.

The biggest practical change is testing frequency. Visual inspection stays on the same quarterly schedule, but microbial testing now has to happen at least once a month during periods of use, not just once a quarter. The law even renames the relevant section to "Cooling towers; maintenance, inspection and testing" to make clear that testing is its own distinct requirement.

When the department has required a biocide application, cleaning, or disinfection, your microbial sample now has to be collected at least two days after that action, so the result reflects normal operating conditions instead of a freshly treated system. For every required microbial test, the qualified person who runs it must report the test date to the department within five days, and the city will publish that date on a public website. When DOB inspects your property, it checks those reported dates against your own records, so the two need to line up. The public access rule was also widened: owners now have to make the results of each inspection and each test available on request, not just inspection results.

Local Law 159 also introduces a brand new seasonal step, subdivision e-1, "Summer cooling tower treatment." Each year, during the warm months when the risk of Legionella growth is higher, you must perform a biocide treatment on each cooling tower according to the department's rules. That is a proactive requirement that did not exist under the old law at all.

Local Law 159 was passed by the City Council on October 9, 2025 and returned unsigned by the Mayor on November 10, 2025, which means it became law without a mayoral signature under the City Charter. The law takes effect 180 days after it becomes law. Counting 180 days from November 10, 2025 puts the effective date in early May of 2026, so you should treat the spring of 2026 as your deadline to have the new routine running.

Monthly testing is roughly three times the sampling cadence you were used to, and each test carries a reporting deadline and a public-facing date that has to match your records. Add the summer biocide treatment and the two-day post-treatment sampling window, and there is a lot more to track over the course of a year. Most owners are not going to keep up with that on their own. Working with a water treatment partner who can handle the monthly sampling, the seasonal treatment, and the reporting on time is the straightforward way to stay compliant and avoid violations. This is the kind of ongoing schedule we manage for our clients, and we would rather get you set up before May than after a missed test.

You can read the complete text of Local Law 159 below.

Click Here to read the City of New York Local Law No. 159 of 2025

Local Law 159 amends Local Law No. 77 of 2015, the original cooling tower law. Click Here to read the original Local Law No. 77