What happens when a Hong Kong cooling tower fails a Legionella test — the Code of Practice action ladder, EMSD's enforcement powers under Cap. 132, and why the duty stays with the building owner.
If your cooling tower fails a Legionella test in Hong Kong, what happens depends on the count. Between 10 and 1,000 cfu/mL, the Code of Practice requires immediate on-line disinfection and a resample — and on EMSD's own sample, that band draws an advisory letter. At 1,000 cfu/mL or above, EMSD issues a statutory nuisance notice under Cap. 132 requiring emergency decontamination, and failing to comply with that notice is an offence. The duty stays with the building owner, even with a contractor engaged.
Legionella is a bacteria that causes Legionnaires' disease, a serious lung infection. It grows in warm water systems — especially cooling towers, which are warm, wet and open to the air. That is why cooling towers are regulated.
The Code of Practice for Fresh Water Cooling Towers (2023 edition) comes in three parts — design and installation, operation and maintenance, and water treatment methods. Part 2 is the one that governs a building already running towers. In practice it means continuous water treatment, regular testing, cleaning and desludging at least every 6 months, and records kept for at least 2 years — all documented. For the detail, see the EMSD Code of Practice explained.
Three bands matter, not two. Below 10 cfu/mL the Code treats Legionella as not detected and you maintain quarterly monitoring. Between 10 and 1,000 cfu/mL you must investigate, review the programme and carry out immediate on-line disinfection, then resample within 3 to 7 days. At 1,000 cfu/mL or above the Code requires immediate emergency decontamination, then a resample within 3 days. Either way you need two consecutive clean samples before returning to the routine regime. We set the full ladder out, with the Code’s own water quality table, in the EMSD Code of Practice explained.
The count itself is only the start. A result at or above 10 cfu/mL puts the tower into a resample loop — on-line disinfection or emergency decontamination, then re-testing until two consecutive clean samples allow a return to routine monitoring — which means extra visits, dosing and sampling on top of the normal programme. At 1,000 cfu/mL or above on EMSD's own sample, the building's location is published alongside the nuisance notice, and the operation and maintenance records for the previous 2 years can be called for on inspection. The first-24-hours sequence is on our emergency response page.
The Code is what you must do. The Public Health and Municipal Services Ordinance (Cap. 132) is what EMSD can do to you, and the two are often confused. With powers delegated from the Director of Food and Environmental Hygiene effective 24 January 2011, EMSD can enter premises and sample your towers at random, and has done so since April 2011. If its sample reads 10–1,000 cfu/mL you receive an advisory letter. If it reads 1,000 cfu/mL or above you receive a nuisance notice requiring emergency decontamination and re-testing within a prescribed period — and failing to comply with that notice is an offence. EMSD also publishes the building locations issued with nuisance notices. In the first half of 2026, 35 of 348 routine surveillance samples came back in the advisory band. Roughly one in ten — every published round is tracked in EMSD cooling tower sampling results.
The Code assigns the work to the O&M contractor and the water treatment service provider. It does not move responsibility for the installation off the owner. Hiring a contractor delegates the task, not the accountability. What protects an owner is two things together: treatment that keeps the water safe, and dated records that prove it. The Code requires those records to be available for inspection on request and kept for at least 2 years.
Run a continuous treatment programme, test regularly, clean on schedule, and keep a written record of every visit — the printable compliance checklist puts those duties on one sheet. Real-time monitoring adds early warning. See cooling tower treatment and Legionella control. If a result has already come back high or a notice has arrived, go to emergency Legionella and EMSD notice response.
It depends on the count. Between 10 and 1,000 cfu/mL the Code of Practice requires investigation, immediate on-line disinfection and a resample within 3 to 7 days. At 1,000 cfu/mL or above it requires immediate emergency decontamination and a resample within 3 days. Either way, you need two consecutive clean samples before returning to the routine monitoring regime.
A statutory notice under the Public Health and Municipal Services Ordinance (Cap. 132), issued when EMSD's own sample of a tower reads 1,000 cfu/mL or above. It requires emergency decontamination and re-testing within a prescribed period, failing to comply with it is an offence, and EMSD publishes the building locations issued with nuisance notices.
Yes. The Code assigns the work to the O&M contractor and the water treatment service provider, but it does not move responsibility for the installation off the owner — hiring a contractor delegates the task, not the accountability. What protects an owner is treatment that keeps the water safe plus dated records, kept for at least 2 years and available for inspection on request.
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