At present, 70 per cent to 80 per cent of the water consumption in Hong Kong is met by Dongjiang water imported to Hong Kong. It has been reported that, with rapid economic growth and urbanisation on the Mainland, the demand for water resources in various provinces and cities is on the rise, and the water sources have been extensively and severely polluted, resulting in a gradual decrease in usable water sources. It has also been reported that the uncertainty in the supply of potable water on the Mainland may affect the supply of Dongjiang water, and it is therefore necessary for the Government to examine the development of new water sources early. In this connection, will the Government inform this Council:
(a) given that the Government has reserved a site in Area 137 of Tseung Kwan O for the construction of a desalination plant, and it is anticipated that the annual output capacity of the desalination plant, upon its coming into operation in 2020, will be about 50 million cubic metres (m3) with the possibility of further increasing to 90 million m3, whether, according to the Government's estimation, it will adjust the ratio of various sources of water supply by then; if it will, of the details, if not, the reasons for that; and
(b) as there are a certain number of water catchment facilities and stormwater storage tanks in Hong Kong (e.g. the water catchment facility in Happy Valley which is under construction and the Hong Kong West Drainage Tunnel which was completed last year) for alleviating the flooding problem in the urban areas, whether the authorities will consider utilising the rainwater collected by these water catchment facilities; if they will, of the details; if not, the reasons for that?
The quality of Dongjiang (DJ) water is closely monitored by Hong Kong's Water Supplies Department (WSD) and the Guangdong authorities (GD). The current Dongjiang Water Supply Agreement (the Agreement) signed with the GD provides that the quality of DJ water supplied to Hong Kong should comply with the national standard set out for Type II waters in the Environmental Quality Standards for Surface Water (GB3838-2002). This is the highest standard applicable for water abstraction for human consumption. The GD has always attached great importance to protecting the quality of DJ water. To ensure that the quality of DJ water supplied to Hong Kong is in compliance with terms and conditions of the Agreement, the GD has proactively implemented various measures including establishment of related laws and instructions as well as implementation of a series of works projects. The regular monitoring results of WSD have indicated that the DJ water quality maintains steady and complying with related standards. After suitable treatment and rigorous disinfection processes at WSD's water treatment works, the fresh water is in full compliance with the requirements set out in the Guidelines of the World Health Organization and is safe for consumption.
On developing new water sources, the Government has been working from time to time on its policies and measures for Hong Kong's fresh water supply. We have also implemented diversified water supply management measures under the Total Water Management Strategy (the Strategy) promulgated in 2008. They include developing seawater desalination and studying water reclamation, grey water re-use and rainwater harvesting.
My reply to the two parts of the question is as follows:
(a) The Planning and Investigation Study of Desalination Plant at Tseung Kwan O commenced in December 2012 and is expected to be completed by end 2014. The study scope covers detailed feasibility study, preliminary design and cost-effectiveness analysis. Subject to the study findings, the Government will draw up a timetable for the construction of the desalination plant, which is expected to commence operation around 2020 at the earliest. The proposed desalination plant will have an output capacity of approximately 50 million m3 per annum, with provisions for future expansion to 90 million m3 per annum.
The Strategy promulgated by the Government in 2008 has mapped out the strategy for a balanced supply and demand of water to support sustainable development in Hong Kong. The Strategy focuses on two major areas, namely water demand management and water supply management. On the management of water demand, the initiatives include stepping up public education, promoting water conservation, promoting the use of water-saving devices, enhancing water leakage control, and extending the use of seawater for toilet flushing. For the supply side management, the initiatives include strengthening the protection of existing water resources and exploring alternative sources of water supply. Other related measures include studying water reclamation, grey water re-use and rainwater harvesting while seawater desalination is only one of the options under consideration.
On the basis of a population of about 7.6 million in 2020 (as projected by the Census and Statistics Department in 2012) and accounting for the estimated savings achieved by various water demand management initiatives, the total fresh water demand will be about 990 million m3 in 2020. With an annual output capacity of 50 million m3, the desalination plant will cover about 5 per cent of the total demand in 2020. The amount of water supplied from other water sources should not exceed the current levels.
(b) To reduce flooding risk in urban areas, the Drainage Services Department (DSD) has adopted the strategy of flow interception and flood storage, involving the construction of drainage tunnels and underground flood storage tanks. In taking forward these infrastructure projects for flood prevention, we have also explored the possibility of reusing the rainwater collected in drainage tunnels and storage tanks.
When studying drainage tunnels, the DSD has examined various options for reusing the rainwater collected. However, all the options would require huge capital investments in building additional tunnels and/or pipe works, together with pumping or storage facilities. The result revealed that re-using rainwater collected in these drainage tunnels would not be cost-effective. As for flood storage tanks, for the purpose of effective flood prevention, the rainwater collected after a rainstorm in flood storage tanks must be discharged as soon as possible in order to prepare for the next rainstorm. Re-using the stored rainwater requires construction of additional storage tanks and associated water transfer facilities. As these facilities would only be used for several rainstorms a year, their cost-effectiveness is doubtful.
Moreover, rainwater running through developed areas would be contaminated by the filth on the surfaces of buildings and roads. The filth is the result of exhaust gases from vehicles travelling on roads, bird droppings on rooftops or animal excreta on the ground, etc. To protect public health, the rainwater collected must be treated before it can be re-used safely. As such, the treatment cost is another factor to be considered.
All in all, re-using rainwater collected through developed areas in drainage system for non-potable uses is not cost-effective. Notwithstanding this, the Government keeps working on its policy and measures for drinking water supply, including harvesting rainwater for irrigation, toilet flushing and other non-potable uses. To date, the Architectural Services Department has installed rainwater harvesting and recycling systems for 33 schools and government facilities such as hospitals, government staff quarters, sports grounds, etc. These systems have been installed and put into operation progressively. A review on their effectiveness is already underway.
Ends/Wednesday, May 22, 2013
Issued at HKT 18:16