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

01 OCT 2022 ALS

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

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

1) Most water samples including clean to dirty matrix
2) Swab

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)

EM0661 Fig 1

Figure 1: Typical suspected legionella colonies on BCYE Agar

EM061 Figure 2

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
Handrail  Swab Legionellae testing

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