It is a common international practice that individual countries / places establish their own set of drinking water standards that is suitable and appropriate to their local context.
In September 2017, the Government adopted the respective guideline values/provisional guideline values in the World Health Organization (“WHO”)’s Guidelines for Drinking-water Quality (“Guidelines”) as the Hong Kong Drinking Water Standards (“HKDWS”).
(A) Revision Framework
The Government undertakes to review systematically the international development and assess the need to trigger review of the HKDWS from time to time. Any revision or update to the HKDWS will follow the following framework: -
(B) Latest Update
With reference to the WHO’s advocacy, the Government commissioned an expert consultant earlier on to conduct a review, including making reference to international practices, to establish a set of drinking water standards suitable for adoption in the local context. Based on the expert consultant’s findings and recommendations, the Government has formulated the latest HKDWS.
With the affirmation from the Drinking Water Safety Advisory Committee (“DWSAC”)1, the Government announced the latest HKDWS (Table 1) on 22 April 2021. The number of water quality parameters in the latest HKDWS is revised from 92 to 60, which includes addition of two new parameters, namely perchlorate and total trihalomethanes, and exclusion of 34 irrelevant parameters.
1 In January 2018, the Government set up a Drinking Water Safety Advisory Committee with members comprising academics and experts of related fields to give advice to Development Bureau on various drinking water safety issues including, inter alia, the review of HKDWS.
In addition, two other lists are established as follows: -
(a) Surveillance List (Table 2) for surveillance monitoring and includes parameters with their levels in the drinking water of Hong Kong at low or even undetectable, and far below a level that would cause adverse health risk, and microbial parameters which serve to indicate the sanitary of drinking water supply systems; and
(b) Watch List (Table 3) for keeping in view of the international development and includes parameters with their potential health risk not yet fully established scientifically.
At the same time, the Government has established the Aesthetic Guidelines (Table 4) in ensuring the aesthetic quality of the drinking water in Hong Kong such as the taste and odour.
(C) Review of Parameters
The generic framework for reviewing parameters in the HKDWS, Surveillance List and Watch List is shown in Figure 1.
Figure 1: Generic framework for reviewing parameters in the HKDWS, Surveillance List and Watch List
Q: How are the latest HKDWS compared with the previous HKDWS?
A: The number of water quality parameters in the latest HKDWS is revised from 92 to 60, which includes addition of two parameters, namely perchlorate and total trihalomethanes, and exclusion of 34 irrelevant parameters.
The newly added parameters have been established in accordance with the latest WHO Guidelines. As for the excluded parameters, they have all along been undetectable under the routine water quality monitoring programme of the WSD, indicating that their levels were negligible, if not nil, in the drinking water of Hong Kong, which they were far below a level that would cause adverse health risk. Nevertheless, the WSD will continue the surveillance of these excluded parameters in the drinking water2.
In addition, with reference to the WHO Guidelines, the Government has adopted more stringent standards for chlorate and dichloroacetate in the latest HKDWS.
2 Except sodium dichloroisocyanurate. It is not used as disinfectant in the water treatment in Hong Kong; and it will not be present in the drinking water in Hong Kong, and therefore will not be included even in the Watch List.