Water Quality Monitoring at Tai Shui Hang

Environmental Protection Department (hereafter referred to as "EPD") has been continuously conducting water quality monitoring at Tai Shui Hang near the West New Territories (WENT) Landfill. Regular water sampling and testing are conducted at four designated water quality monitoring points (namely TSH1, TSH2, TSH3 and TSH4) as shown in the figure below. The EPD collects water samples twice per month during, before and after the wet season (i.e. March to October of each year) and once per month during the dry season (i.e. November to February of the following year). The water quality in Tai Shui Hang is monitored and assessed with reference to the Water Quality Index (WQI) used by the EPD.
 
Locations of Water Quality Monitoring Points at Tai Shui Hang

Locations of Water Quality Monitoring Points at Tai Shui Hang

Water Quality Index (WQI) for Rivers in Hong Kong

Water Quality Index (WQI) is a numerical value used to gauge and denote, based on monitoring data, the overall state of health of rivers and streams in Hong Kong. The WQI is calculated based on three key water quality parameters: dissolved oxygen, five-day biochemical oxygen demand (BOD5) and ammonia-nitrogen levels. The index is classified into five grades (Excellent, Good, Fair, Bad and Very Bad) and the scoring is based on the calculation method shown in the table below.

Calculation of WQI

No. of points awarded

Dissolved Oxygen
(% saturation)

BOD5
(mg/L)

Ammonia Nitrogen
(mg/L)

1

91 – 110

< 3

< 0.5

2

71 – 90

111 – 120

3.1 – 6.0

0.5 – 1.0

3

51 – 70

121 – 130

6.1 – 9.0

1.1 – 2.0

4

31 – 50

9.1 – 15.0

2.1 – 5.0

5

< 30 or > 130

> 15.0

> 5.0

 

All parameters carry equal weighting, and the WQI is the sum of points converted from these three parameters. The WQI values range from 3 to 15, corresponding to the following gradings of river water quality conditions.

WQI gradings

WQI

River Water Quality Condition

3.0 – 4.5

Excellent

4.6 – 7.5

Good

7.6 – 10.5

Fair

10.6 – 13.5

Bad

13.6 – 15.0

Very Bad

 

For further details about the WQI assessment and grading, please visit this website.

 

Water Quality Monitoring Data at Tai Shui Hang (2024 to May 2025)

Water Quality Monitoring Point (1)

Dissolved Oxygen

(% saturation)

5-day Biochemical Oxygen Demand (mg/L)

 Ammonia Nitrogen (mg/L) WQI River Water Quality Condition
Date of sample taken : 9/1/2024
TSH1 114.2 <2 0.31 4 Excellent
TSH2 150 <2 0.38 7 Good
TSH3 102.6 <2 <0.01 3 Excellent
TSH4 99.8 <2 <0.01 3 Excellent
Date of sample taken : 20/2/2024
TSH1 97.8 <2 0.17 3 Excellent
TSH2 96.9 <2 0.43 3 Excellent
TSH3 108.8 <2 0.072 3 Excellent
TSH4 97.5 <2 0.039 3 Excellent
Date of sample taken : 15/3/2024
TSH1 85.1 <2 0.14 4 Excellent
TSH2 66.7 <2 0.22 5 Good
TSH3 93.6 <2 0.017 3 Excellent
TSH4 91.1 <2 0.013 3 Excellent
Date of sample taken : 25/3/2024
TSH1 108.7 <2 0.056 3 Excellent
TSH2 105.3 <2 0.38 3 Excellent
TSH3 94.1 <2 <0.01 3 Excellent
TSH4 87 <2 0.02 4 Excellent
Date of sample taken : 3/4/2024
TSH1 98.1 <2 0.1 3 Excellent
TSH2 89.4 <2 0.79 5 Good
TSH3 97.2 <2 0.015 3 Excellent
TSH4 90.1 <2 0.027 4 Excellent
Date of sample taken : 18/4/2024
TSH1 125.7 <2 0.063 5 Good
TSH2 98.6 <2 0.059 3 Excellent
TSH3 87 <2 0.012 4 Excellent
TSH4 87 <2 <0.01 4 Excellent
Date of sample taken : 9/5/2024
TSH1 83.6 <2 <0.01 4 Excellent
TSH2 86.6 <2 <0.01 4 Excellent
TSH3 83.5 <2 0.021 4 Excellent
TSH4 84.2 <2 0.026 4 Excellent
Date of sample taken : 17/5/2024
TSH1 126.2 <2 0.064 5 Good
TSH2 119.6 2.1 0.11 4 Excellent
TSH3 114.5 <2 0.053 4 Excellent
TSH4 93.1 <2 0.066 3 Excellent
Date of sample taken : 12/6/2024
TSH1 83.4 <2 0.024 4 Excellent
TSH2 82.5 2.2 <0.01 4 Excellent
TSH3 93.4 <2 0.025 3 Excellent
TSH4 92.2 <2 <0.01 3 Excellent
Date of sample taken : 20/6/2024
TSH1 88.5 <2 <0.01 4 Excellent
TSH2 93.9 <2 0.01 3 Excellent
TSH3 91.3 <2 0.019 3 Excellent
TSH4 89.4 <2 <0.01 4 Excellent
Date of sample taken : 3/7/2024
TSH1 92.2 <2 0.021 3 Excellent
TSH2 110.1 <2 <0.01 3 Excellent
TSH3 95.9 <2 0.02 3 Excellent
TSH4 94.5 <2 0.1 3 Excellent
Date of sample taken : 23/7/2024
TSH1 81.8 <2 0.14 4 Excellent
TSH2 91.9 <2 0.12 3 Excellent
TSH3 92.5 <2 0.072 3 Excellent
TSH4 91.8 <2 0.092 3 Excellent
Date of sample taken : 7/8/2024
TSH1 84 <2 0.042 4 Excellent
TSH2 81.7 <2 0.051 4 Excellent
TSH3 102.9 <2 0.02 3 Excellent
TSH4 99.8 <2 0.024 3 Excellent
Date of sample taken : 23/8/2024
TSH1 94.3 <2 0.061 3 Excellent
TSH2 95.5 <2 0.037 3 Excellent
TSH3 95.2 <2 0.043 3 Excellent
TSH4 93.9 <2 0.068 3 Excellent
Date of sample taken : 11/9/2024
TSH1 95.4 <2 0.092 3 Excellent
TSH2 94.3 <2 0.2 3 Excellent
TSH3 94 <2 0.03 3 Excellent
TSH4 92.2 <2 <0.01 3 Excellent
Date of sample taken : 26/9/2024
TSH1 88.6 <2 0.011 4 Excellent
TSH2 73.8 <2 0.067 4 Excellent
TSH3 92.4 <2 0.03 3 Excellent
TSH4 92.1 <2 0.019 3 Excellent
Date of sample taken : 7/10/2024
TSH1 88.8 <2 0.15 4 Excellent
TSH2 107.6 <2 0.074 3 Excellent
TSH3 97.3 <2 0.011 3 Excellent
TSH4 97.5 <2 <0.01 3 Excellent
Date of sample taken : 16/10/2024
TSH1 91.6 <2 0.031 3 Excellent
TSH2 95.5 <2 0.022 3 Excellent
TSH3 97.5 <2 0.06 3 Excellent
TSH4 98.1 <2 0.07 3 Excellent
Date of sample taken : 12/11/2024
TSH1 80.2 <2 0.072 4 Excellent
TSH2 79.8 <2 0.064 4 Excellent
TSH3 95.9 <2 0.062 3 Excellent
TSH4 95.4 <2 0.031 3 Excellent
Date of sample taken : 4/12/2024
TSH1 109.4 <2 0.041 3 Excellent
TSH2 108.3 <2 0.022 3 Excellent
TSH3 94.1 <2 <0.01 3 Excellent
TSH4 92 <2 <0.01 3 Excellent
Date of sample taken : 9/1/2025
TSH1 92.8 <2 0.03 3 Excellent
TSH2 102.1 <2 1.6 5 Good
TSH3 96.5 <2 <0.01 3 Excellent
TSH4 94.3 <2 0.013 3 Excellent
Date of sample taken : 27/2/2025
TSH1 96.7 <2 0.13 3 Excellent
TSH2 90.5 <2 0.15 3 Excellent
TSH3 91.4 <2 0.02 3 Excellent
TSH4 87.9 <2 0.04 4 Excellent
Date of sample taken : 11/3/2025
TSH1 99.1 <2 0.22 3 Excellent
TSH2 80.9 <2 0.3 4 Excellent
TSH3 98.8 <2 0.01 3 Excellent
TSH4 93.5 <2 0.02 3 Excellent
Date of sample taken : 19/3/2025
TSH1 86.8 <2 0.15 4 Excellent
TSH2 84.5 <2 0.16 4 Excellent
TSH3 95.9 <2 0.02 3 Excellent
TSH4 92.4 <2 0.01 3 Excellent
Date of sample taken : 16/4/2025
TSH1 86.6 <2 0.19 4 Excellent
TSH2 88 <2 0.2 4 Excellent
TSH3 103.2 <2 <0.01 3 Excellent
TSH4 93.1 <2 0.12 3 Excellent
Date of sample taken : 24/4/2025
TSH1 100.4 <2 0.11 3 Excellent
TSH2 92.7 <2 0.27 3 Excellent
TSH3 71 18 5.09 12 Bad (2)
TSH4 66.3 26 5.89 13 Bad (2)
Date of sample taken : 13/5/2025 (2)
TSH1 83.3 <2 0.15 4 Excellent
TSH2 83.7 <2 0.1 4 Excellent
TSH3 64.9 <2 0.98 6 Good
TSH4 70.2 3 1.2 7 Good
Date of sample taken : 23/5/2025 (2)
TSH1 102.8 <2 0.04 3 Excellent
TSH2 105.1 <2 0.07 3 Excellent
TSH3 92.7 <2 0.19 3 Excellent
TSH4 69.2 <2 0.6 6 Good
Date of sample taken : 9/6/2025
TSH1 125 <2 0.03 5 Good
TSH2 117 <2 0.07 4 Excellent
TSH3 83 <2 0.27 4 Excellent
TSH4 85 <2 0.28 4 Excellent
Date of sample taken : 25/6/2025
TSH1 83 <2 0.06 4 Excellent
TSH2 88 <2 0.09 4 Excellent
TSH3 94 <2 0.07 3 Excellent
TSH4 88 <2 0.12 4 Excellent

 

Remarks :

  1. The contract for the WENT Landfill does not specify requirements for water quality monitoring at Tai Shui Hang. If unusual changes in water quality are detected, the EPD will take follow-up actions.
  2. On 24 April 2025, the ammonia-nitrogen levels at the upstream monitoring points of Tai Shui Hang (TSH3 and TSH4) ranged from 5.09 to 5.89 mg/L, receiving the lowest WQI scoring (i.e., 5 points). The BOD5 levels were 18 and 26 mg/L, receiving the lowest WQI scoring (i.e., 5 points). However, subsequent monitoring showed that the water quality at both monitoring locations had returned to "Excellent" to "Good" levels. For further details, please refer to the discussion paper for the meeting of the Food, Environment and Hygiene Committee, Tuen Mun District Council held on 19 June 2025.

Please click here for monitoring results of year 2018 to 2023. 

 

EPD staff collect water samples from Tai Shui Hang (TSH3)

EPD staff obtains water sample from Tai Shui Hang (TSH3)

 

Upstream of Tai Shui Hang (TSH4)

Upstream of Tai Shui Hang
 
 

Back to top Back