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Enhanced Water Quality Monitoring Programme - Annual Summary of Water Quality Statistics in 2018

The Water Supplies Department (WSD) launched the Enhanced Water Quality Monitoring Programme (the Enhanced Programme) in December 2017. Being one of the five components of the Action Plan for Enhancing Drinking Water Safety in Hong Kong promulgated in September 2017, the Enhanced Programme is to monitor the general condition of drinking water quality at consumers' taps in Hong Kong and collect local water quality data for reviewing the Hong Kong Drinking Water Standards (HKDWS) in three to five years' time. Under the Enhanced Programme, the WSD engaged an independent consultant to randomly select premises from all water accounts in the 18 district council districts (DCDs) in Hong Kong according to the population size of DCDs based on a sampling rate of eight premises per 5 000-100 000 people for collecting water samples. In 20181, 672 premises were selected. Water samples were collected from the drinking water taps of the selected premises to test for six metals, viz. antimony, cadmium, chromium, copper, lead and nickel, which might be present in an internal plumbing system, using a two-tier sampling protocol detailed as follows:

Tier 1 – Random Day Time (RDT) sampling: to monitor the water quality in respect of the six metals. 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 exceedance is found 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.

A summary of the water quality statistics of the water samples collected from the 672 premises is tabulated in Table 1 below.

Table 1: Summary of Annual Water Quality Statistics of the Enhanced Programme in 2018

  Minimum Maximum Average 95th percentile Standard Value Compliance of water quality with the 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)		 <3 460 21 78 2 000 ✓
Lead
(µg/L)		 <1 14 <1 1 10 ✓
Nickel
(µg/L)		 <1 290 3 5 70 ✓

* 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.

Besides, the key analyses of the above water quality statistics in 2018 are as below:

  1. The maximum contents of antimony, cadmium, and chromium of all RDT samples were below the reporting limit2 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 value and the 95th percentiles among all RDT samples were 460 µg/L and 78 µg/L respectively 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.
  3. For lead, the maximum value of all RDT samples was 14 µg/L and two RDT samples exceeded the standard value of 10 µg/L.
  4. For nickel, the maximum value of all RDT samples was 290 µg/L and two RDT samples exceeded the standard value of 70 µg/L.
  5. In respect of the exceedances as mentioned in (c) and (d) above, according to the two-tier sampling protocol of the Enhanced Programme, the corresponding 30MS samples for the four RDT samples with exceedance were tested to verify the lead/nickel exposure of the concerned consumers and the results of all the four 30MS samples complied with the standards, representing that the drinking water quality of the four concerned premises complied with the HKDWS. The exceedances of the RDT samples were likely due to unduly long stagnation time before sampling or sporadic presence of metal particles.
  6. Since the 95th percentiles of RDT samples of lead and nickel were 1 µg/L and 5 µg/L respectively which were all well below their corresponding standard values of 10 µg/L and 70 µg/L in the HKDWS, the risk of exceedance of lead and nickel contents in the drinking water at consumers’ taps in Hong Kong is low.

The test results of the water samples showed that contents of the six metals in the drinking water of all premises tested were in compliance with the corresponding standard values of the HKDWS.

As regards the few cases of exceedance in RDT samples that were likely due to unduly long stagnation time before sampling or sporadic presence of metal particles, the WSD would continue to conduct publicity and public education to advise the consumers to flush the taps after long periods of stagnation (for instance, overnight stagnation) before using the water for drinking or cooking, which is a common and effective practice to lower the metal contents in the drinking water.

Please visit the webpage on Enhanced Water Quality Monitoring Programme - Annual Water Quality Statistics in 18 District Council Districts in 2018 for more details.

Note:

1. Water samples from 672 premises were taken during the period from 25 December 2017 to 31 December 2018.

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