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Enhanced Water Quality Monitoring Programme - Annual Summary of Water Quality Statistics in 2019

The Water Supplies Department (WSD) launched the Enhanced Water Quality Monitoring Programme (the 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 drinking water quality at consumers' taps in Hong Kong and will collect local water quality data over a period of three to five years for review of the Hong Kong Drinking Water Standards (HKDWS). Under the Enhanced Programme, the WSD has engaged an independent consultant to select premises randomly from all water accounts of the 18 district council districts (DCDs) in Hong Kong based on a sampling rate of 8 premises per 5 000-100 000 people. In 2019, drinking water samples were collected from the drinking water taps of 663¹ selected premises using a two-tier sampling protocol to test for six metals, viz. antimony, cadmium, chromium, copper, lead and nickel, which might be present in an internal plumbing system as follows:

Tier 1 – Random Day Time (RDT) sampling: to monitor the drinking water quality in respect of the six metals in Hong Kong. A 1-litre unflushed sample will be randomly taken during the daytime.

Tier 2 – 30-minute stagnation (30MS) sampling: to verify the metal exposure of consumers (will only be tested if there is exceedance in the Tier 1 sample). The tap will first be flushed for 5 minutes and then stagnated for 30 minutes. After stagnation, a 1-litre unflushed sample will be taken at the tap.

The statistics of the monitoring results of the drinking water samples collected in 2019 under the Enhanced Programme is summarised in Table 1 below.

Table 1: Statistics of Monitoring Results in 2019 under the Enhanced Programme

* A “✓” indicates compliance of drinking water quality with the HKDWS in all selected premises based on the two-tier water sampling test results of the Enhanced Programme, i.e. the parameter will be regarded as complying with the HKDWS if (i) there is no exceedance in the Tier 1-RDT sample or (ii) there is no exceedance in the Tier 2-30 MS sample in case there is exceedance in the Tier 1 sample.

An analysis of the monitoring results in 2019 under the Enhanced Programme is as below:

1. The maximum value of antimony among all RDT samples was below the reporting limit² of < 1 µg/L. It indicates that the antimony content in the drinking water at consumers’ taps in Hong Kong is very low.
2. For cadmium, the maximum value and the 95^th percentile among all RDT samples were 2 µg/L and <1 µg/L respectively, both of which were below the standard value of 3 µg/L in the HKDWS.  In fact, the 99^th percentile was also below the reporting limit of < 1 μg/L. It indicates that the risk of exceedance of cadmium content in the drinking water at consumers’ taps in Hong Kong is very low.
3. For chromium, the maximum value and the 95^th percentile among all RDT samples were 3 µg/L and <1 µg/L respectively, both of which were well below the standard value of 50 µg/L in the HKDWS.  In fact, the 99^th percentile was also below the reporting limit of < 1 μg/L.  It indicates that the risk of exceedance of chromium content in the drinking water at consumers’ taps in Hong Kong is very low.
4. For copper, the maximum value and the 95^th percentile among all RDT samples were 390 µg/L and 63 µg/L respectively, both of 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. 
5. For nickel, the maximum value and the 95^th percentile among all RDT samples were 52 µg/L and 4 µg/L respectively, both of 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.
6. For lead, six RDT samples exceeded the standard value of 10 µg/L with a maximum value of 19 µg/L whilst no exceedance was found in the corresponding Tier-2 30MS samples. This represents that the drinking water quality of the six concerned premises complied with the HKDWS.  The exceedances of the RDT samples were likely due to (i) unduly long stagnation time before sampling or (ii) sporadic presence of metal particles.  Since the 95^th percentile among the RDT samples was 2 µg/L which was well below the standard value of 10 µg/L in the HKDWS, the risk of exceedance of lead content in the drinking water at consumers’ taps in Hong Kong is low.

Overall, the monitoring results showed that the contents of the six metals in the drinking water of all premises randomly selected for sampling under the Enhanced Programme in 2019 were all in compliance with the corresponding standard values of the HKDWS.

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

Note:

1. In fact, a total of 664 premises were selected in 2019 for sampling under the Enhanced Programme. However, one of the visits on the last day of December 2019 was unsuccessful and substitution visit within 2019 was not possible.
2. Reporting limit is the lowest level within an analytical method’s operation range.