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LCQ18: Incidents of fresh water contamination caused by water works

Following is a question by the Hon Wilson Or and a written reply by the Secretary for the Development, Mr Michael Wong, in the Legislative Council today (January 17):
 
Question:
 
It was reported that two incidents occurred one after the other in November last year in which the water works arranged by the Water Supplies Department (WSD) caused contamination of fresh water and odour emitting from it. A number of public rental housing (PRH) estates, Home Ownership Scheme (HOS) courts and private housing estates in Kwai Tsing, Tsuen Wan and Sha Tin were affected. Some residents said that they had developed gastrointestinal symptoms after drinking the contaminated fresh water. In this connection, will the Government inform this Council:
 
(1) whether the WSD will take water samples for laboratory tests from the residential flats affected by the aforesaid incidents, and make public the substances that caused the emission of odour from the fresh water and the potential hazards posed to human health by such substances; if so, of the details; if not, the reasons for that;
 
(2) whether the WSD issued guidelines to the estate management personnel of the PRH estates, HOS courts and private housing estates affected by the aforesaid incidents on cleaning the fresh water storage tanks and water supply pipes in the buildings concerned to ensure that the fresh water supplied to the residents conforms with the safety standards; if so, of the details; if not, the reasons for that;
 
(3) whether the WSD has, in the light of the aforesaid incidents, reviewed the relevant monitoring procedures to avoid the recurrence of incidents of contamination of fresh water by water works; if so, of the details; if not, the reasons for that; and
 
(4) apart from the provision of temporary water supply to residents affected by incidents of fresh water contamination, whether the WSD has formulated new contingency measures in the light of the experience gained from the aforesaid incidents, so as to ensure the safety of fresh water supplied to residents; if so, of the details; if not, the reasons for that, and whether the WSD will formulate the relevant measures expeditiously?
 
Reply:
 
President,
    
With regard to the Hon Wilson Or's questions on the two water quality incidents, their causes are as follows:
 
(i) Unpleasant odour in drinking water in some areas of Kwai Chung and Tsuen Wan
 
The incident happened between November 18 and 20 last year. The preliminary probable cause of the incident was due to the application of a protective coating material, which had been approved for use in potable water installation works, by a maintenance contractor of the Water Supplies Department (WSD) for the maintenance of the floor slab of the eastern compartment of the Tsuen Wan Fresh Water Service Reservoir. The coating material contains volatile organic compounds (VOCs) which have an unpleasant odour. The service reservoir has the eastern and western compartments which are separated by a central division wall. Since there were two openings between the top of the division wall and the roof of the service reservoir, part of VOCs got into the western compartment, which was in operation, through the openings on top of the division wall and dissolved in the drinking water which was then distributed to customers.
 
The Director of Water Supplies has set up an independent investigation team which will soon submit a detailed investigation report on the incident.
 
(ii) Turbidity of drinking water in some areas of Fo Tan, Sha Tin
 
The incident, which happened in the evening of November 29 last year, was caused by the preparation work carried out by a contractor of the WSD, including inspection and operation of gate valves, for replacing government mains at Tai Po Road (Sha Tin Section) near Wo Che Estate. Owing to the change of water flow arising from operating the gate valves, some sediments inside the water mains were stirred up, causing turbidity in the drinking water in some areas of Fo Tan.
 
The WSD spared no effort in following up the above two water quality incidents in order to restore the quality of drinking water supply to residents as soon as possible. During the incidents, the WSD deployed water wagons and water tanks near the affected estates to provide drinking water to the residents in need. The WSD also proactively contacted the management offices of related estates and offered technical support to them when necessary in order to drain away the residual water in the inside service.
 
The reply to the four parts of the Hon Wilson Or's questions is as follows:
 
(1) For the incident of unpleasant odour in drinking water in some areas of Kwai Chung and Tsuen Wan, the WSD took water samples from the outlet pipe of the western compartment of the Tsuen Wan Fresh Water Service Reservoir during the incident for rapid toxicity test. The test result was negative, i.e. non-toxic. The water samples were also tested for the contents of the 15 health-related VOCs parameters recommended in the World Health Organization's Guidelines for Drinking-water Quality (WHO Guidelines). All results complied with the WHO Guidelines. Owing to the low odour detection threshold of VOCs, even if their concentrations comply with relevant the WHO Guidelines, a very low VOC concentration in the drinking water would still be perceivable by the customers. However, it would not cause any health hazard. Immediately afterwards, the WSD issued a press release to give an account of the initial test results on the drinking water quality and the preliminary probable cause of the incident. 
 
For the incident of turbidity of drinking water in some areas of Fo Tan, Sha Tin, some sediments in the water mains were stirred up during the operation of gate valves, resulting in turbidity in the drinking water. Nevertheless, the sediments in the water mains were mainly hydrated lime, trace of iron or minerals, which would not cause health hazard.
 
(2) During the above two incidents, the WSD promptly contacted the property management personnel of the affected estates to provide appropriate technical support so as to assist them in cleansing water storage tanks and water pipes, etc, within the estates. To facilitate property management personnel to take prompt and appropriate contingency measures when similar water quality incidents occur in future, the WSD is preparing relevant guidelines for reference by property management companies or owners’ organisations.
 
(3) In the light of the above two water quality incidents, the WSD is reviewing its construction works procedures to identify room for improvements in every aspect that might affect the water quality. For the unpleasant odour in drinking water in some areas of Kwai Chung and Tsuen Wan, the WSD has set up an independent investigation team which will not only look into the cause of the incident, but also recommend improvement measures to prevent recurrence of similar incidents.  In regard to the turbidity of drinking water in some areas of Fo Tan, Sha Tin, the WSD is also reviewing the monitoring mechanism for the contractors and engineering personnel during the construction stage. The above reviews are substantially completed. The WSD is now revising the relevant guidelines with a view to implementing the improvement measures under the revised guidelines as soon as possible.
 
(4) In respect of the contingency measures for water quality incidents, the WSD will review and formulate enhancement measures in various aspects, including the arrangements of releasing information, the provision of temporary fresh water supply during emergency incidents and the collection of water samples for testing.

Ends/Wednesday, January 17, 2018
Issued at HKT 15:39

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