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Enhanced Water Quality Monitoring Programme - Annual Summary of Water Quality Statistics in 2022

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 monitors the concentration of six metals, viz. antimony, cadmium, chromium, copper, lead and nickel in drinking water at consumers’ taps of randomly selected premises.  It 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”).  Since 17 May 2021, residual chlorine and Escherichia coli (“E. coli”) have been included in the Enhanced Programme.

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 drinking 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 drinking water sample is collected for testing residual chlorine.  The tap is then disinfected and further flushed for at least two minutes, and a drinking water sample is collected afterwards for testing E. coli.

In 2022, 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 people1.  While 672 premises had been identified for sample collection in the year, the Enhanced Programme was suspended from 13 January to 9 May 2022 due to the COVID-19 pandemic, and as a result only 460 premises2 were visited for sample collection.

The statistics of the test results of the drinking water samples collected in 2022 under the Enhanced Programme is summarised in Table 1  below.

Table 1: Statistics of Monitoring Results% in 2022

Parameter 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) <3 750 30 100 ≤2 000 ✓
Lead (µg/L) <1 30 <1 1 ≤10 #
Nickel (µg/L) <1 62 2 4 ≤70 ✓
Residual Chlorine (mg/L) <0.1^ 1.2 0.5 0.9 ≤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.  

#   One lead exceedance case was found.  Upon investigation, the exceedance was due to the lack of proper installation and maintenance of water using apparatus in the premises concerned.  The compliance rate with the HKDWS for lead content in 2022 was 99.8% while the cumulative compliance rate since the launching of the Enhanced Programme was 99.96%.

^   Although there were depletion of residual chlorine level (i.e. <0.1 mg/L) found in two premises, E. coli was not detected.  As such, the risk of fecal contamination in the drinking water of the premises concerned is very low.

@ cfu = colony forming unit

The analysis of the monitoring results in 2022 under the Enhanced Programme is as below:-

  1. For antimony, cadmium and chromium, all the results were below the reporting limit3 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 750 µg/L and 100 µg/L respectively, which were respectively below and well 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, there was one exceedance case found and the test results of the corresponding RDT and 30MS samples were 15 µg/L and 13 µg/L respectively, both exceeding the standard value of 10 µg/L in the HKDWS. The investigation revealed that a water dispenser in the premises concerned had not been equipped with a non-return valve and the filter unit of the water dispenser had not been replaced for a long time.  As a result, there was backflow of substances accumulated in the filter unit, including lead, to the internal water supply system, causing contamination to the drinking water of the premises concerned.

    There were also four other premises with RDT samples found exceeding the standard value of 10 µg/L with a maximum value of 30 µg/L but the corresponding 30MS samples were found complying with the HKDWS4.

    The 95th percentile value of all RDT samples was 1 µg/L which was well below the standard value of 10 µg/L.  Coupled with the fact that there were only two isolated exceedance cases5 (one case each in 2021 and 2022) out of some 2 500 samples tested so far under the Enhanced Programme, 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 62 µg/L and 4 µg/L respectively, which were respectively below and well 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 95th percentile values were 1.2 mg/L and 0.9 mg/L respectively, both of which were well 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 very low.
  6. All drinking water samples were found to be free of E.coli which fully complied with the HKDWS. It indicates that the risk of fecal contamination in the drinking water at consumers’ taps in Hong Kong is very low.

Overall, with the exception of a lead exceedance case associated with the lack of proper installation and maintenance of water using apparatus in the premises concerned, the drinking water quality of all premises randomly selected under the Enhanced Programme in 2022 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. According to the sampling rate, drinking water samples will be collected from a total of about 670 randomly selected premises each year.
  2. Making reference to overseas practices, the shortfall in sampling due to programme suspension would not be made up.
  3. Reporting limit is the lowest level within an analytical method’s operation range.
  4. 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.
  5. The two exceedance cases were either due to the lack of proper maintenance of the internal plumbing system or the lack of proper installation and maintenance of water using apparatus in the premises concerned.

Past Summary of Water Quality Statistics: