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Enhanced Water Quality Monitoring Programme - Annual Summary of Water Quality Statistics in 2023

The Water Supplies Department (“WSD”) launched the Enhanced Water Quality Monitoring Programme (“Enhanced Programme”) in December 2017, as one of the five components of the Action Plan for Enhancing Drinking Water Safety in Hong Kong promulgated in September 2017.  The Enhanced Programme currently monitors the concentration of six metals, viz. antimony, cadmium, chromium, copper, lead and nickel, as well as residual chlorine and Escherichia coli (“E. coli”) in drinking water at consumers’ taps of randomly selected premises.  The Enhanced Programme also serves to collect local drinking water quality data for review of the standard values of the six metals in the Hong Kong Drinking Water Standards (“HKDWS”).  

The monitoring of six metals adopts the following two-tier sampling protocol: -

Tier 1 – Random Day Time (“RDT”) sampling

The purpose is to monitor the water quality in respect of the six metals.  An unflushed sample is randomly collected during daytime.

Tier 2 – 30-minute stagnation (“30MS”) sampling

The purpose is to verify the metal exposure of consumers in case exceedance is found in the Tier 1 RDT sample.  The tap is first flushed for five minutes and then stagnated for 30 minutes.  After stagnation, an unflushed sample is collected. 

After collecting the samples for testing the six metals, the tap is flushed for at least two minutes and a sample is collected for testing residual chlorine.  The tap is then disinfected and further flushed for at least two minutes, and a sample is collected afterwards for testing E. coli.

In 2023, the WSD continued to engage an independent consultant to select premises randomly from all water accounts in the 18 district council (“DC”) districts.  The number of premises to be selected from each DC district was determined based on the population therein and a sampling rate of eight premises per 5 000 to 100 000 people.  Drinking water samples were collected from 661 randomly selected premises in 2023.

The statistics of the test results of the water samples collected in 2023 under the Enhanced Programme is summarised in Table 1 below.

Table 1: Statistics of Monitoring Results# in 2023

Minimum Maximum Average 95th percentile Standard value in HKDWS Compliance with HKDWS*
Antimony (µg/L) <1 <1 <1 <1 ≤20 ✓
Cadmium (µg/L) <1 <1 <1 <1 ≤3 ✓
Chromium (µg/L) <1 <1 <1 <1 ≤50 ✓
Copper (µg/L) <3 610 20 60 ≤2 000 ✓
Lead (µg/L) <1 23 <1 1 ≤10 ✓
Nickel (µg/L) <1 24 2 4 ≤70 ✓
Residual Chlorine (mg/L) 0.1 1.4 0.6 1.0 ≤5 ✓
E. coli (cfu@/100 mL) 0 0 0 0 0 ✓

#   RDT results for six metals are presented.

*   A “✓” indicates 100% compliance of drinking water quality with the HKDWS in all randomly selected premises based on the corresponding testing protocol. For the two-tier water sampling test results of the six metal parameters, the test result will be regarded as complying with the HKDWS if (i) there is no exceedance found in RDT sample or (ii) there is no exceedance found in the 30MS sample in case the RDT sample fails.

@ cfu = colony forming unit

The analysis of the monitoring results in 2023 under the Enhanced Programme is given below: -

  1. For antimony, cadmium and chromium, all the results were below the reporting limit1 of <1 µg/L.  It indicates that the contents of antimony, cadmium and chromium in the drinking water at consumers’ taps in Hong Kong are very low.
  2. For copper, the maximum and the 95th percentile values were 610 µg/L and 60 µg/L respectively which were below the standard value of 2 000 µg/L in the HKDWS.  It indicates that the risk of exceedance of copper content in the drinking water at consumers’ taps in Hong Kong is low.
  3. For lead, four RDT samples exceeded the standard value of 10 µg/L with a maximum value of 23 µg/L but the corresponding 30MS samples were found complying with the HKDWS. This represents that the drinking water quality of these premises complied with the HKDWS.  The exceedance of the RDT samples was likely due to unduly long stagnation time before sampling or sporadic presence of metal particles.  The 95th percentile value of all RDT samples was 1 µg/L which was below the standard value of 10 µg/L.  It indicates that the risk of exceedance of lead content in the drinking water at consumers’ taps in Hong Kong is low.
  4. For nickel, the maximum and the 95th percentile values were 24 µg/L and 4 µg/L respectively, which were below the standard value of 70 µg/L in the HKDWS. It indicates that the risk of exceedance of nickel content in the drinking water at consumers’ taps in Hong Kong is low.
  5. For residual chlorine, the maximum and the 95th percentile values were 1.4 mg/L and 1.0 mg/L respectively, which were below the standard value of 5 mg/L in the HKDWS.  It indicates that the risk of exceedance of residual chlorine content in the drinking water at consumers’ taps in Hong Kong is low.
  6. All drinking water samples collected were found to be free of E. coli which fully complied with the HKDWS. It indicates that the risk of faecal contamination in the drinking water at consumers’ taps in Hong Kong is very low.

Overall, the drinking water quality of all premises randomly selected under the Enhanced Programme in 2023 complied with the HKDWS in respect of the six metals, residual chlorine and E. coli.

Please visit the webpage on Enhanced Water Quality Monitoring Programme – Annual Water Quality Statistics in 18 District Council Districts for more details.

Note:

  1. Reporting limit is the lowest level within an analytical method’s operation range.

Past Summary of Water Quality Statistics: