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NYC cooling towers · 24 RCNY §8-05(f)(5), Table 8-1

A positive Legionella result: what to do, and by when

Table 8-1 of the DOHMH rules sets what follows a Legionella culture result, level by level; from 10 CFU/ml it calls for disinfection within 24 hours. The table counts the notice to DOHMH from receiving the result, and the other hour clocks are read the same way. Since September 4, 2026, Chapter 206 of 2026 says each step is taken as soon as possible, and no later than its 24 or 48 hours.

Check a building freeLast verified Oct 19, 2026

Table 8-1

What each result asks

Legionella culture results in colony-forming units per milliliter (CFU/ml), as 24 RCNY §8-05(f)(5), Table 8-1 sets them. Each retest is read against the table again until a result is under 10.
Result (CFU/ml)What follows
Under 10Not detected: keep the water chemistry and biocide levels. Detected: review the water treatment program and adjust the chemistry and biocide levels if needed.
10 to 99Start disinfection within 24 hours, with more biocide or a different one; review the treatment program; retest within 3 to 7 days.
100 to 999As for 10 to 99, and a visual inspection to judge whether the tower needs cleaning and further disinfection.
1,000 or moreStart disinfection within 24 hours; full remediation within 48 hours; notify DOHMH within 24 hours of receiving the result; review the program; retest within 3 to 7 days.

What it asks

What the owner has to do

  1. Start disinfection within 24 hoursAt 10 CFU/ml or more: more biocide or a different biocide, started within 24 hours, and a review of the treatment program. Record when the work was done.24 RCNY §8-05(f)(5), Table 8-1
  2. Inspect from 100 CFU/mlFrom 100 CFU/ml, a visual inspection also judges whether the tower needs cleaning and further disinfection.Table 8-1, level 3
  3. Remediate from 1,000 CFU/mlFull remediation within 48 hours: hyperhalogenate, drain, clean and flush the tower.Table 8-1, level 4
  4. Tell DOHMH from 1,000 CFU/mlA notice to DOHMH within 24 hours of receiving the result. The State’s rule asks the same of an owner above 1,000 CFU/ml: a notice to the local health department, which in New York City is DOHMH, and DOHMH notifies the State.Table 8-1, level 4; 10 NYCRR §4-1.6(a)
  5. Retest within 3 to 7 daysTable 8-1 says “within 3-7 days” without saying from what, so a retest 3 to 7 days after both the result and the disinfection fits either reading. Each retest is read against the table again.Table 8-1
  6. A high HPC is its own triggerA weekly HPC or dip slide of 10,000 CFU/ml or more calls for disinfectant residual checks three times a day until on target for 24 hours, a Legionella sample if that takes more than 3 days, and a retest 48 hours after.24 RCNY §8-05(f)(5), Table 8-2

Deadlines

The clocks

  • Disinfection started, 10 CFU/ml or moreWithin 24 hours of the resultTable 8-1
  • Notice to DOHMH, 1,000 CFU/ml or moreWithin 24 hours of receiving the resultTable 8-1, level 4
  • Full remediation, 1,000 CFU/ml or moreWithin 48 hours of the resultTable 8-1, level 4
  • RetestWithin 3 to 7 daysTable 8-1
  • Each step, since September 4, 2026As soon as possible, and no later than its hoursAdmin Code §17-194.1(e)(2)

Penalties

What a violation costs

First violation / repeat, per the penalty schedule, with DOHMH’s violation code where it has one. Since May 8, 2026 there is no cure period at inspection.

  • Disinfect within 24 hours of a positive Legionella result24 RCNY §8-05(f)(5), Table 8-1$2,000 / $4,000 · AH8U
  • Visual inspection to judge whether the tower needs cleaning24 RCNY §8-05(f)(5), Table 8-1, level 3$2,000 / $4,000 · AH8U
  • Full remediation within 48 hours: hyperhalogenate, drain, clean, flush24 RCNY §8-05(f)(5), Table 8-1, level 4$2,000 / $4,000 · AH8U
  • Notify DOHMH within 24 hours of a result of 1,000 CFU/ml or more24 RCNY §8-05(f)(5), Table 8-1, level 4$2,000 / $4,000 · AH8U
  • Retest 3 to 7 days after a positive result24 RCNY §8-05(f)(5), Table 8-1$2,000 / $4,000 · AH8U

FAQ

Questions owners ask

When does the 24-hour clock start?

Table 8-1 counts the notice to DOHMH from receiving the result, not from the sample, and the other hour clocks are read the same way. Ask the lab to send results to the owner or manager and to the qualified person at the same time, so the hours are not lost in one inbox.

Is a positive result a violation?

Not by itself. Not acting on it in time is: DOHMH’s code for a corrective action not taken after a bacteriological result is AH8U.

Does the State need its own notice?

Not from the owner in New York City. The State’s rule has the owner notify the local health department within 24 hours of a result above 1,000 CFU/ml, and that department, DOHMH here, notifies the State. So the notice to DOHMH within 24 hours is the one the owner sends.

What changed on September 4, 2026?

Chapter 206 of 2026 added “as soon as possible” to these steps: the 24 and 48 hours are the latest a step may come, not a time to wait.

Your building

See the clock DOHMH sees

Type the address. The free check shows the last sample date DOHMH has, the days left on the 31-day clock, the inspections and any OATH summons on the lot.

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Sources · Last verified Oct 19, 2026

A plain-English summary of the rules, not legal advice. The rule text and DOHMH’s guidance decide; check them before you act.