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 sufficient local drinking water quality data over a period of three to five years for review of the standard values of the six metals in the Hong Kong Drinking Water Standards (“HKDWS”).  Starting from 17 May 2021, the scope of the Enhanced Programme has been expanded to cover the monitoring of residual chlorine and Escherichia coli (“E. coli”).

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 taken 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 taken.

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 for testing E. coli.

The WSD has engaged an independent consultant to select premises randomly from all water accounts in the 18 district council (“DC”) districts of Hong Kong according to the population of each DC district and based on a sampling rate of eight premises per 5 000 to 100 000 people^[1].  In 2021, drinking water samples were collected from 675 randomly selected premises.

The statistics of the test results of the drinking water samples collected in 2021 under the Enhanced Programme is summarised in Table 1 (for six metals) and Table 2 (for residual chlorine and E. coli) below.  

Table 1: Statistics of RDT Monitoring Results for the Six Metals in 2021   

*   A “✓” indicates 100% compliance of drinking water quality with the HKDWS in all randomly selected premises based on the two-tier water sampling test results of the Enhanced Programme, under which 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 contamination of the internal plumbing system. The compliance rate with HKDWS for lead content in 2021 was 99.9% while the cumulative compliance rate since the launching of the Enhanced Programme was 99.95%.

Table 2: Statistics of Monitoring Results for Residual Chlorine and E. coli in 2021

Note: cfu – colony forming unit

*   A “✓” indicates 100% compliance of drinking water quality with the HKDWS in all randomly selected premises.

#  Although there were depletion of residual chlorine level (i.e. <0.1 mg/L) found in some premises, no E. coli was detected.  As such, the risk of fecal contamination in the drinking water of the premises concerned is very low.

The analysis of the monitoring results in 2021 under the Enhanced Programme is as below:-

1. For antimony, all the results were below the reporting limit^[2] of <1 µg/L. It indicates that the contents of antimony in the drinking water at consumers’ taps in Hong Kong are very low.
2. For cadmium and chromium, their maximum values were well below the standard values in the HKDWS respectively. Also, the 99^th percentile value was below the reporting limit of <1 µg/L.  It indicates that the respective risks of exceedance of cadmium and chromium in the drinking water at consumers’ taps in Hong Kong are very low.
3. For copper, the maximum value and the 95^th percentile value were 620 µg/L and 120 µg/L respectively, both of which were 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.

4. For lead, there was one exceedance case found and the test results of the corresponding RDT and 30MS samples were 17 µg/L and 12 µg/L respectively, both exceeding the standard value of 10 µg/L in the HKDWS. This was in fact the first exceedance case reported under the Enhanced Programme since its launch in late 2017.  The investigation conducted by the qualified person engaged by the premises owner revealed that the water tanks in the internal plumbing system of the building concerned had not been cleansed for an extended period of time and had metal fragments left behind, which was the cause of the lead exceedance case.

   Another RDT sample of 12 µg/L in the other premises was found exceeded the standard value of 10 µg/L in the HKDWS whilst no exceedance was found in the corresponding 30MS sample.  This represents that the drinking water quality of this premises complied with the HKDWS.  The exceedance of the RDT sample was likely due to unduly long stagnation time before sampling or sporadic presence of metal particles.

   It should be noted that the 95^th percentile value of the RDT samples was 1 µg/L which was well below the standard value of 10 µg/L in the HKDWS.  Coupled with the fact that there was only one exceedance case out of some 2 110 samples tested so far under the Enhanced Programme, which can be regarded as an isolated case due to the lack of proper maintenance of the internal plumbing system, the risk of exceedance of lead content in the drinking water at consumers’ taps in Hong Kong is low.

5. For nickel, two RDT samples exceeded the standard value of 70 µg/L with a maximum value of 98 µg/L but no exceedance was found in the corresponding 30MS samples. According to the testing protocol, the drinking water quality of the two premises concerned complied with the HKDWS.  The exceedance found in the RDT sample was likely due to unduly long stagnation time before sampling or sporadic presence of metal particles.  Since the 95^th percentile value of the RDT samples was 6 µg/L which was well below the standard value of 70 µg/L in the HKDWS, the risk of exceedance of nickel content in the drinking water at consumers’ taps in Hong Kong is low.
6. For residual chlorine, the maximum value and 95^th percentile value were 1.1 mg/L and 0.8 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 low. 
7. For E. coli, 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 maintenance of the internal plumbing system, the drinking water quality of all premises randomly selected under the Enhanced Programme in 2021 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. Reporting limit is the lowest level within an analytical method’s operation range.