The Water Quality Objective (WQO) is the basic benchmark by which the EPD measures and analyses Hong Kong's beach water quality. It is a standard, reached after extensive epidemiological studies in Hong Kong in the late 1980s, which specifies acceptable levels for the presence of certain key bacteria in beach water. The WQO states that the level of E. coli bacteria present in water samples should not exceed 180 per 100mL. This figure for individual beaches is calculated by taking the geometric mean of all samples collected during the bathing season from March to the end of October. Samples are taken at least three times a month, at intervals of from three to 14 days.
The WQO standard is linked to E. coli bacteria because the presence of these bacteria was found to have the best correlation with illness rates (specifically skin and gastrointestinal illnesses) associated with swimming in Hong Kong. It is relatively simple, by observing the levels of E. coli in beach water, to estimate the precise health risks of swimming at beaches.
Sampling takes place at all gazetted beaches at least once a week during the bathing season, and at least once a month outside that period. The four beaches that remain open all year continue to be monitored weekly throughout the year.
To make sure samples are genuinely representative of day-to-day fluctuations in beach water quality, they are taken on randomly selected days, including weekends and public holidays.
EPD staff take the samples from water at thigh to waist level, a little distance away from the shoreline. Once collected, the water samples are kept at a steady temperature of 4 degrees Celsius until they are ready to be tested at the EPD's laboratory. Besides these core samples, staff also collect samples from streams and storm drains that flow into the bathing area or nearby. These samples are used to assess the impact, if any, of these external water sources on beach water quality.
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Beach monitoring frequencies
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Beach
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Monitoring frequency
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| Bathing season | Non-bathing season | |
| Gazetted beaches open all year round * | 4 - 6 times per month | 4 - 6 times per month |
| Other gazetted beaches | 4 - 6 times per month |
At least once per month |
| Non-gazetted beaches | 2 -3 times per month | Once per month |
| * Deep Water Bay, Clear Water Bay Second, Silverstrand and Golden Beaches | ||
The EPD uses its own laboratory, located in Wanchai and staffed by experienced and well-qualified scientists and technicians. Each of the dozens of samples relayed to the EPD's laboratory is measured for pH, salinity and turbidity. At the same time, samples are analysed for the presence of E. coli bacteria. This process involves filtering each water sample through a membrane to trap bacteria, and incubating the membrane for a period of 18 to 24 hours. The resulting specimens of E. coli bacteria are then counted. All the scientific information gathered during this process is entered into an extensive databank for retrieval on demand. The total time for the process of testing and analysing samples has now been reduced to just one and a half days, allowing the EPD to get updated information to the public very quickly indeed.
[Image of Laboratory testing in progress]
[Image of Bacteria after incubation]
[Image of Laboratory analysis of beach water samples]
Two primary purposes lie behind the laboratory analysis of samples:
- grading beaches. This involves assigning each beach a grade based
on recent results of sample tests. The EPD's beach grading system is
designed to give the public an up-to-date picture of the state of any
beach at any time during the year, so they can make informed decisions
about when and where to swim.
- ranking beaches. The EPD ranks beaches on an annual basis, and rankings reflect the overall standards of any given beach across the entire bathing season. This information is particularly useful for seeing longer term trends in water quality across different areas of Hong Kong
Beach Grading System
Because beach grading is designed to reflect the current state of a beach,
grading is based on the geometric mean E. coli levels of the five
most recent samples. On the basis of these samples, beaches are graded
into one of four categories (see the table below). Since sampling at gazetted
beaches takes place at least once a week during the bathing season, the
beach grading system generally reflects the state of a beach across the
previous month or so. However, if the most recent sample from a beach
shows E. coli levels exceeding 1600 per 100mL, this result overrides
the geometric mean figure and the beach is immediately given Grade 4,
representing very poor water quality. In this way, the beach grading system
can react quickly to sudden fluctuations in water quality that may arise
from periods of heavy rain, for example, or localised pollution incidents.
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Grade
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Beach
Water Quality
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E.
coli count per 100mL*
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Minor
illness rate**
(Cases per 1000 swimmers) |
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1
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Good
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<=24
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UD
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2
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Fair
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25-180
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<=10
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3
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Poor
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181- 610
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11-15
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4
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Very
Poor
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>610
or last reading >1,600 |
>15
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| * Except
otherwise indicated, the E. coli level is the geometric mean
of the 5 most recent sampling occasions. ** Skin and gastrointestinal illnesses UD Undetectable |
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The beach annual ranking system is based on the geometric mean E. coli level of all the samples collected from the bathing area of each beach across the entire bathing season. As the table below shows, this information is used to ascertain whether each beach complied with WQO standards. WQO compliance is a simple yes/no status, but the EPD also uses test results to issue a more fine-grained ranking. Beaches that comply with WQO standards are further assigned either 'Good' or 'Fair' status, depending on E. coli count, while beaches that do not comply are divided into 'Poor' and 'Very Poor' to reflect the severity of their problems.
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Rank
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E. coli count per 100mL* |
Minor
illness rate**
(Cases per 1000 swimmers) |
WQO
Compliance
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Good
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<=24
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UD
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Complied
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Fair
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25-180
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<=10
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Poor
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181-610
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11-15
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Not
complied
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Very
Poor
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>610
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>15
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| * Geometric
mean E. coli count calculated based on all data collected
during the bathing season. ** Skin and gastrointestinal illnesses UD Undetectable |
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