It is internationally recognised that access to clean and safe drinking water is a fundamental human need and right. The quality of drinking water can be analysed and assessed by testing contaminants in four aspects: microbiological, chemical, radiological and physical.
The WHO has recommended a "health-based" target to ensure drinking water safety. Most consumers assess the quality and acceptability of drinking water via its appearance, odour and taste. It is the WHO's advocacy and international practice that individual places establish their own drinking water standards suitable and appropriate to their local context. Since September 2017, the HKSAR Government has established the Hong Kong Drinking Water Standards (HKDWS) and continues to conduct related studies and reviews. In April 2021, the government announced the revised HKDWS, which now covers 60 water quality parameters.
Unclean drinking water is the vector of transmission of diseases. Microbial contaminants, including pathogenic bacteria, viruses, protozoa and worms, are the most common culprits. These pathogens mainly cause gastroenteritis symptoms, such as temporary diarrhoea, abdominal pain and vomiting. Raw water before water treatment also contains various chemicals. Taking fluoride as an example, which is a natural mineral and an important component for healthy bones and teeth: insufficient fluoride intake increases the risk of tooth decay, but excessive amounts can lead to fluorosis and even poisoning. Therefore, health-based standards for drinking water ensure that the risks of each quality parameter are scientifically assessed, in order to select the most appropriate parameters for water testing.
The WHO has defined the following four categories of 'health-based' targets: health outcome, water quality, specified technology, and performance. Hong Kong’s drinking water is safe for consumption when the test results of individual parameters fall within the standards of the HKDWS.
The appearance, odour, and taste of water can be affected by the microbiological, chemical and physical constituents in drinking water. Although these constituents may not have direct health implications, consumers may regard drinking water with any objectionable appearance, taste and odour to be unsafe for consumption. Therefore, when assessing the quality of drinking water, aesthetic aspects must also be taken into consideration.
The WHO first published the Guidelines for Drinking-water Quality (the Guidelines) in 1984. Until 2022, four editions of the Guidelines have been published, with the most recent editions being released in 2004 and 2011. With reference to the Water Safety Plan (WSP) of the 2004 Guidelines, the WSD developed and implemented its own WSP to review the city’s water supply system and drinking water quality using risk assessment and management strategies. In 2017, the WSD reviewed the WSP and developed an integrated "Drinking Water Quality Management System" to enhance the WSP. This system also outlines the water quality policy and management principles of the WSD. (See the article "Water Safety and Its Monitoring" in this chapter for details)
In September 2017, the HKSAR Government adopted the WHO’s guideline values and provisional guideline values of its 2011 edition as the HKDWS. Subsequently, the government commissioned an expert consultant to review and develop the drinking water standards more appropriate to Hong Kong’s situation. The recommendations were accepted by the Drinking Water Safety Advisory Committee and promulgated in April 2021. The number of parameters was revised to 60 to serve as the standard for routine drinking water quality monitoring. Additionally, two new sets of parameters, namely the Surveillance List and the Watch List, were introduced. The former is used for surveillance monitoring and includes microbial parameters to indicate the sanitary of the drinking water supply system, while the latter is used for reviewing the latest international scientific developments. Aesthetic guidelines have also been added as a water quality indicator.
| Chemical Category | Radiation Category | Microbiological Category | Physical Category | |
|---|---|---|---|---|
| Parameters of HKDWS | 57 parameters, including metals, disinfectants, disinfection by-products, pesticides, organic and inorganic chemicals | 2 parameters: Gross alpha (α) activity, Gross beta (ẞ) activity | 1 parameter: Escherichia coli | / |
| Parameters for the Surveillance List | Total 37 parameters | / | 4 parameters: Coliform, Cryptosporidium, Giardia, heterotrophic plate count | / |
| Parameters for the Watch List | 686 parameters | 1 parameter: Radon | / | / |
| Aesthetic Guidelines | 5 parameters: aluminium, iron, manganese, zinc, 2-methyl-isoborneol | / | / | 5 parameters: colour, odour, pH, taste, turbidity |