Legionella can be found in natural aqueous environment, such as lakes, rivers, ponds, soil and man-made water systems (e.g. fresh water cooling towers), and can grow well in warm water (20 to 45 degrees Celsius). Proper design, operation and maintenance of fresh water cooling towers could prevent proliferation of legionella.
It is the basic responsibility of owners of fresh water cooling towers to properly operate and maintain their cooling towers and, for this purpose, they should arrange regular inspections, timely maintenance and periodic testing of the water quality of their cooling towers in accordance with the Code of Practice for Fresh Water Cooling Towers issued by EMSD.
Water testing for legionella concentration (in terms of total legionella count) is a means to check effectiveness of water treatment to prevent its proliferation in the cooling tower. It is a normal practice in operation and maintenance for tower owners to obtain feedback from testing results to see how effective is the maintenance and take necessary remedial action so as to upkeep the system and water quality at normal operational conditions.
Cooling towers with water samples found with total legionella count at or above the upper threshold of 1 000 cfu/ml shall undergo emergency decontamination. The test result also hints to major failure of water treatment facilities and/or operation requiring urgent rectification by the owners of the cooling towers.
Separately, as legionella may exist in aqueous environments and elevated concentrations may occur sporadically in cooling towers, it is not uncommon to detect legionella in the range between 10 cfu/ml (note 1) and 1 000 cfu/ml. Such cases will more often reflect intermittent inadequate vigilance of tower owners in carrying out routine maintenance and water treatment programmes and works. Like other normal operation and maintenance works, test results will provide a corrective feedback signal to tower owners to review and adjust the operation and maintenance to the system so that the water quality can be restored to normal by minimizing its bacterial contents.
EMSD will carry out random inspections of fresh water cooling towers and collect water samples for bacterial testings for the purpose of monitoring if the owners of cooling towers have properly discharged their responsibility to properly operate and maintain the cooling towers to ensure that the quality of the cooling tower water is at a satisfactory level. EMSD will take the following regulatory actions according to the water sample test results -
If cooling tower water samples are found with total legionella count at or above the upper threshold of 1 000cfu/ml, EMSD will issue a nuisance notice under the Public Health and Municipal Services Ordinance, Cap. 132 (PHMSO) to the owner of the cooling tower requiring the owner to carry out emergency decontamination as per the Code of Practice for Fresh Water Cooling Towers issued by EMSD. Failure to comply with the requirements as stipulated in the nuisance notice will be guilty of an offence.
If cooling tower water samples are found with total legionella count in the range of between 10 to 1 000 cfu/ml, EMSD will issue an advisory letter to ask the owner of the cooling tower to take actions to restore the water quality to normal by minimizing its bacterial contents through on-line disinfection as per the Code of Practice for Fresh Water Cooling Towers issued by EMSD.
| Total (From Jan up to mid-Dec 2024) | |
|---|---|
| No. of water samples from fresh water cooling towers tested by EMSD (No. of buildings involved) |
839 (517) |
| No. of water samples with total legionella count at or above the upper threshold (i.e. 1 000 cfu/ml) with nuisance notices issued | 21 |
| No. of water samples detected with total legionella count between 10 and 1 000 cfu/ml | 164 |
| Total (From Jan up to mid-Dec 2024) | |
|---|---|
| No. of water samples from fresh water cooling towers tested. (No. of buildings involved) |
11 (6) |
| No. of water samples with total legionella count at or above the upper threshold (i.e. 1 000 cfu/ml) with nuisance notices issued | 0 |
| No. of water samples detected with total legionella count between 10 and 1 000 cfu/ml | 3 |
Please click here for building locations of fresh water cooling towers detected with total legionella count ≥ 1 000cfu/ml with nuisance notices issued in the past 3 months period, if any [PDF format (203KB)] (Updated on 20 December 2024).
Please click here for previous annual statistics since 2011 [PDF format (89KB)] (Updated on 8 January 2024).