Safety Standard

How to determine the water in your home safe to drink?

WHO Guidelines for Drinking Water Quality

The Guidelines cover a broad range of chemicals that can affect drinking water quality but not all chemicals will be relevant within a country. To learn more about the list of chemicals, their guideline values and its hazards in drinking water, please click here.

Hong Kong Drinking Water Standards (HKDWS)

The Government currently adopts the corresponding guideline values / provisional guidline values in the 4th edition of the WHO”s Guidelines published in 2011 as the Hong Kong Drinking Water Standards. Details can be found here.

HKDWS Parameters of Heavy Metals

Metals

Potential Health Hazards

Acceptance Criteria (in μg/L)

Antimony

Antimony trioxide is possibly carcinogenic to humans.

Acceptance Criteria (in μg/L):

≤ 20

Arsenic

Long-term exposure to arsenic in drinking-water is causally related to increased risks of cancer in the skin, lungs, bladder and kidney, as well as other skin changes, such as hyperkeratosis and pigmentation changes.

Acceptance Criteria (in μg/L):

≤ 10

Barium

Barium has been shown to cause nephropathy in laboratory animals.

Acceptance Criteria (in μg/L):

≤ 700

Boron

Short- and long-term oral exposures to boric acid or borax in laboratory animals have demonstrated that the male reproductive tract is a consistent target of toxicity.

Acceptance Criteria (in μg/L):

≤ 2400

Cadmium

Classified as probably carcinogenic to humans, cadmium accumulates primarily in the kidneys and has a long biological half-life in humans of 10 to 35 years.

Acceptance Criteria (in μg/L):

≤ 3

Chromium

It is classified as human carcinogen.

Acceptance Criteria (in μg/L):

≤ 50

Copper

At high concentration level, copper imparts an undesirable bitter taste to water and may impact the colour of water. Copper contaminated drinking water brings gastrointestinal effects.

Acceptance Criteria (in μg/L):

≤ 2000

Lead

Exposure to lead is associated with a wide range of effects, including various neurodevelopmental effects, mortality (mainly due to cardiovascular diseases), impaired renal function, hypertension, impaired fertility and adverse pregnancy outcomes.

Acceptance Criteria (in μg/L):

≤ 10

Mercury

The toxic effects are seen primarily in haemorrhagic gastritis and colitis; the ultimate damage is to the kidney.

Acceptance Criteria (in μg/L):

≤ 6

Nickel

Metallic nickel is possibly carcinogenic. In an animal study with administered nickel, the integrity and performance of male and female reproductive systems, growth and development of offspring and post-implantation/perinatal lethality are found.

Acceptance Criteria (in μg/L):

≤ 70

Selenium

Symptoms in people with excessive selenium included gastrointestinal disturbances, discolouration of the skin, decayed teeth, hair or nail loss, nail abnormalities and changes in peripheral nerves.

Acceptance Criteria (in μg/L):

≤ 40

Uranium

Nephritis is the primary chemically induced effect of uranium in humans.

Acceptance Criteria (in μg/L):

≤ 30

Source: Health Hazards information from World Health Organization

HKDWS Physical and Chemical Parameters

Physical and Chemical Parameters

Explanation

Acceptance Criteria

pH

pH is a measure of how acidic/basic water. pH ranges from 0 to 14, with 7 being neural. pH of less than 7 indicates acidity, whereas a pH greater than 7 indicates a base solution. Pure water is neutral, with a pH close to 7.0 at 25°C. Normal rainfall has a pH of approximately 5.6 (slightly acidic) owing to atmospheric carbon dioxide gas. Safe ranges of pH for drinking water are from 6.5 to 8.5 for domestic use.

A high pH makes the taste bitter and decreases the effectiveness of the chlorine disinfection. Low-pH water will corrode or dissolve metals and other substances.

Acceptance Criteria:

≥ 6.5 and ≤ 9.2 (at 25°C)

Electrical Conductivity (EC)

EC is a measure of the ability of a solution to carry or conduct an electrical current. Conductivity in water is affected by the presence of inorganic dissolved solids such as chloride, nitrate, sulfate, and phosphate anions (ions that carry a negative charge) or sodium, magnesium, calcium, iron, and aluminum cations (ions that carry a positive charge).

Acceptance Criteria:

≤ 300 μS/cm (at 25°C)

Colour

Colour is graded on scale of 0 (clear) to 70 Hazen unit (HU). Pure water is colourless, which is equivalent to 0 Hazen unit.

Acceptance Criteria:

≤ 5 HU

Turbidity

Turbidity is a measure of the ability of light to pass through water. The particulates can provide hiding places for harmful microorganisms and thereby shield them from the disinfection process. Suspended particles provide adsorption media for heavy metals such as mercury, chromium, lead, cadmium, and many hazardous organic pollutants.

Turbidity more than 5 NTU can be visible to the average person while turbidity in muddy water, it exceeds 100 NTU.

Acceptance Criteria:

≤ 3.0 NTU

Chlorine Residual

Chlorine (Cl₂) does not occur naturally in water but is added to water and wastewater for disinfection. While chlorine itself is a toxic gas, in dilute aqueous solution, it is not harmful to human health. In drinking water, a residual of about 0.2 mg/L is optimal. The residual concentration which is maintained in the water distribution system ensures good sanitary quality of water.

Acceptance Criteria:

> 0 and ≤ 1.5 mg/L

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