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EnviroMail 61 Hong Kong
Updated Legionella testing methods for water and swab
In late June 2022, Water Supplies Department (WSD) updated the requirements for the commissioning of
fresh water plumbing system
For example, evaporative cooling towers and humidifiers of air-conditioning systems, hot and cold water systems, whirlpool or spas, even decorative water fountains, home respiratory therapy devices, humidifiers and mist machines.
ALS provides below accredited legionella testing methods with the latest edition.
| Tests | Latest edition | Previous edition |
| Legionella | AS 3896: 2017 (ALS code: EM016a) |
AS/NZS 3896:1998 (ALS code: EM016) |
| ISO 11731: 2017 (ALS code: EM016B/EM039) |
ISO 11731-2: 2014 (superseded) |
Summary for the comparison between AS methods:
| Method | AS 3896 : 2017 | AS/NZS 3896 : 1998 |
| Application | All water samples: Dirty: cooling tower water, wastewater Clean: recreational, potable and natural water |
Dirty: cooling tower water and wastewater ONLY |
| Reporting limit | 10 cfu/mL | 10 cfu/mL |
| Treatment technique | Direct, heat, acid Additional acid treatment to increase accuracy |
Direct, heat, acid |
| Turnaround time |
Summary for the comparison between ISO methods:
| Method | ISO 11731 :2017 | ISO 11731-2 :2004 |
| Application |
1) Most water samples including clean to dirty matrix |
Clean water only such as recreational and potable water |
| Reporting limit | EM016B: 0.1 cfu/mL
EM039: Clean water: 1-100 cfu/L Dirty water: 10 cfu/mL Clean swab: 10 cfu/swab Dirty swab: 100 cfu/swab |
0.1 cfu/mL (100 cfu/L) |
| Treatment technique | Specific treatment and medica used for various sample matrix (avoid masking other colonies to Legionellae colonies) | Single type of acid treatment only |
| Turnaround time | 12 days (2 days of confirmation included) | |
Figure 1: Typical suspected legionella colonies on BCYE Agar
Figure 2: Sterile Swab for surface legionella test.
Since ALS has provided different legionella testing methods, client please state the detailed sample type, ALS method code or testing method with edition on the submission form when submitting samples. For example:
| Sample description / ID | Sample type | Test(s) required |
| Water feature | Water | Legionellae testing (EM016a) |
| Handrail | Swab | Legionellae testing (EM039HL) |
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If you have any questions relating to vessel discharge water analysis, please contact
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