WSD Circular Letter No. 5/2023
Water Sampling Protocol for Commissioning of Fresh Water Plumbing System
Introduction
At Enviro Labs, we provide comprehensive water sampling and testing services tailored to meet the latest requirements for commissioning freshwater plumbing systems. Adhering to the standards set forth by the Hong Kong Water Supplies Department (WSD) Circular Letter No. 5/2023, our services ensure compliance, safety, and peace of mind for plumbers, property developers, contractors, and facility managers
Overview of Testing Requirements
As per WSD Circular Letter No. 5/2023, water sampling protocols for commissioning new freshwater plumbing systems have been updated to streamline procedures and maintain strict quality standards. The protocol applies to all new plumbing works and systems submitted with Form WWO 46 Part IV from September 18, 2023, onward. Key aspects include:
-
Sampling Procedure
-
Flush water taps for at least two minutes to remove impurities.
-
Disinfect taps following ISO 19458 protocols.
-
Collect a single 250 ml sterile water sample for microbial tests, covering both Heterotrophic Plate Count (HPC) and E. coli analysis.
-
Additional samples are collected for testing physical, chemical, and metal parameters after a 30-minute or 6-hour stagnation period.
-
-
Acceptance Criteria
Testing ensures the water quality meets the following standards:-
Physical and Chemical
-
Turbidity: ≤ 3.0 NTU
-
Colour: ≤ 5 Hazen Units
-
pH: Between 6.5 and 9.5
-
Free Chlorine: ≤ 1.5 mg/L
-
Conductivity: ≤ 500 µS/cm
-
-
Metal Content：
-
Lead: ≤ 10 µg/L
-
Chromium: ≤ 50 µg/L
-
Nickel: ≤ 70 µg/L
-
Cadmium: ≤ 3 µg/L
-
Copper: ≤ 2000 µg/L
-
Antimony: ≤ 20 µg/L
-
-
Microbiological Standards:
-
Heterotrophic Plate Count: ≤ 20 cfu/mL
-
E. coli: 0 cfu/100 mL
-
-
How to choose stagnation period (30-minute or 6-hour)?
-
6-Hour Stagnation Period
-
Applicable for: New plumbing systems in unoccupied buildings.
-
Procedure:
-
Flush the tap for at least 2 minutes, then disinfect it.
-
Apply protective measures, such as covering the tap, and let water stagnate for 6 hours before sampling.
-
-
Purpose: This extended stagnation period simulates conditions of prolonged inactivity, assessing the potential leaching of metals from the plumbing system.
-
-
30-Minute Stagnation Period
-
Applicable for: Existing plumbing systems in occupied buildings or village houses.
-
Procedure:
-
Flush the tap for at least 3 minutes, reinstall the strainer, and disinfect it.
-
Let the water stagnate for 30 minutes before sampling.
-
-
Purpose: This shorter stagnation period reflects typical daily usage patterns, evaluating water quality under regular operating conditions.
-
Criteria for Choosing Stagnation Period
The stagnation period is selected based on the occupancy status of the building:
-
Unoccupied Buildings: Use a 6-hour stagnation period to assess worst-case scenarios.
-
Occupied Buildings: Use a 30-minute stagnation period to simulate realistic usage and ensure compliance with water quality standards for daily consumption.
WSD has the final decision-making authority to determine the stagnation period based on the actual situation.
Why Choose Enviro Labs?
Enviro Labs offers HOKLAS-accredited testing services that strictly adhere to WSD requirements. Our offerings include:
-
Trained and certified personnel for sampling and testing.
-
Properly documented reports with photographic records for submission.
-
Standard and express turnaround options to fit project timelines.
Get Started Today
Ensure your project complies with WSD standards. Contact Enviro Labs for professional water sampling and testing services designed to meet your specific needs. Call us for more information.
References
1. WSD Circular Letter No. 5/2023