Following is a question by the Hon Chan Hak-kan and a written reply by the Secretary for Development, Mr Paul Chan, in the Legislative Council today (April 29):
In reply to my question, the authorities said on February 26 this year that the Drainage Services Department (DSD) was planning to expand the Shek Wu Hui Sewage Treatment Works (SWH STW) and upgrade its treatment technology and, taking the opportunity, the Water Supplies Department (WSD) had in collaboration with the relevant departments studied the feasibility of producing reclaimed water of acceptable standards through further processing of the tertiary treated sewage effluent from SWH STW for supplying the district for non-potable uses (including irrigation, toilet flushing, etc.). In this connection, will the Government inform this Council:
(1) of the quantity of seawater used for toilet flushing and the average quantity of seawater used by each household for toilet flushing, in each of the past three years;
(2) of the number of households or population currently using potable water for toilet flushing, with a breakdown by the 18 District Council districts;
(3) of the estimated annual number of customers who can be supplied with the reclaimed water produced by SWH STW for toilet flushing;
(4) given that the authorities plan to produce reclaimed water of acceptable standards through further processing of the tertiary treated sewage effluent from SWH STW, of the procedures involved in such "further processing";
(5) whether it knows the overseas countries or regions in which reclaimed water is more commonly used for toilet flushing; the respective quality standards adopted in those countries or regions for reclaimed water;
(6) of the current quality standards adopted in Hong Kong for reclaimed water, and the authorities' basis or rationale for setting those standards; and
(7) given that a member of the Advisory Committee on Water Resources and Quality of Water Supplies has pointed out that in foreign countries, reclaimed water which has undergone only relatively simple secondary treatment and processing is able to meet the needs for toilet flushing and landscape irrigation in metropolitan areas, whether it has studied if the tertiary treated sewage effluent from SWH STW can be used, without further treatment, for toilet flushing; if the outcome of the study is in the negative, of the reasons for that?
Developing reclaimed water is one of the initiatives for managing water supply under the Total Water Management Strategy adopted by the Government in 2008 in pursuance of sustainable use of water resources in Hong Kong. The results of two pilot schemes for reclaimed water conducted by the Government at Ngong Ping and Shek Wu Hui demonstrate that it is technically feasible to use water reclaimed from tertiary treated effluent of sewage treatment works for non-potable uses.
To cope with the development of North East New Territories (NENT) New Development Areas, the DSD needs to expand SWH STW and upgrade its treatment technology to tertiary level to deal with the additional effluent load as well as to comply with the standard set by the Environmental Protection Department for discharging treated effluent to Deep Bay. The WSD has taken this opportunity to jointly study with departments concerned the feasibility of producing reclaimed water by further processing tertiary treated effluent of SWH STW for non-potable uses, including toilet flushing, within the NENT region. The findings show that supplying reclaimed water within this region is cost-effective as the additional process required for producing reclaimed water from tertiary treated effluent is relatively simple.
The WSD has started planning for the infrastructure works for supplying reclaimed water for non-potable uses within the NENT region. Supply of reclaimed water is expected to commence in 2022.
My reply to the seven parts of the question is as follows:
(1) The quantity of seawater used for toilet flushing in the past three years is tabled below:
Year Quantity of seawater used
(million cubic metres)
As there is no water meter for measuring the quantity of seawater used for toilet flushing by each household, the average annual quantity of seawater used by each household is not available.
(2) There are around 33 500 domestic accounts, involving about 20% of the population in Hong Kong, using potable water for toilet flushing. The distribution of these accounts is as follows:
No. of Domestic
Region Potable Water for
Hong Kong and Islands Region 8 700
Kowloon Region 700
New Territories East Region 9 400
New Territories West Region 14 700
Total 33 500
*Note 1: Normally, for supply of potable water for toilet flushing, only one meter is installed for all consumers, both domestic and non-domestic, in a building. The WSD does not maintain any statistics on the distribution of domestic flushing accounts by 18 District Council districts.
*Note 2: The total number of domestic accounts using potable water for toilet flushing includes mixed accounts (i.e. both domestic and non-domestic consumers) that use potable water for toilet flushing.)
(3) As mentioned above, the WSD has started planning the infrastructures for supplying reclaimed water for non-potable uses within the NENT region. According to the current estimate, around 450 000 people will have access to reclaimed water for toilet flushing.
(4) "Further processing" refers to the process of adding chlorine to the tertiary treated effluent of SWH STP for disinfection and decolourisation purpose before distributing it for use by the public.
(5) and (6) While it is common practice in many places around the world, including Singapore, the United States, etc., to use reclaimed water for irrigation and other non-potable purposes, potable water is generally used for toilet flushing. Using reclaimed water for toilet flushing remains uncommon because the buildings abroad generally do not have separate internal plumbing systems for flushing water, which is a pre-requisite for using reclaimed water for toilet flushing. The case for Hong Kong is different. We have been using seawater for toilet flushing for years. Our buildings generally have separate internal plumbing systems for toilet flushing, which facilitate the conversion into using reclaimed water for toilet flushing.
The water quality standards for reclaimed water around the world are formulated with due consideration for its scope of uses (e.g. industrial use, irrigation), its sensory impact (e.g. color and odor) and safeguarding public health. When formulating the water quality standards for reclaimed water for non-potable uses in Hong Kong, we have also considered these factors and made reference to the standards of reclaimed water around the world to ensure that the reclaimed water is hygienic and safe for public use. The key parameters for the water quality standards of reclaimed water in Hong Kong are set out in the Annex.
(7) As mentioned in paragraph (4) above, the tertiary treated effluent from the SWH STW must be disinfected and decolourised by adding chlorine. This is a mandatory process before the reclaimed water can be distributed for public use. In fact, the seawater supplied by the WSD for toilet flushing also needs to undergo chlorination before being distributed for public use.
Ends/Wednesday, April 29, 2015
Issued at HKT 12:18