Sustainable Infrastructure: Towards A Diversified HK Water Supply
By David von Eiff 19 March, 2020
How can Hong Kong further secure its water supply? Dr von Eiff shares from Civic Exchange's latest water report
While the combination of local yield, Dongjiang water and seawater flushing has formed the backbone of Hong Kong’s water supply since the late 1960s, the Water Supplies Department (WSD) demonstrated in the Total Water Management Strategy 2019 that it is beginning to pursue alternative sources, including desalinated water and recycled water (see image below), to ensure a sustainable water supply for Hong Kong.
How sustainable do you think these water sources are? Civic Exchange’s newly published report, “Modernising Hong Kong’s Water Management Policy Part II: Sustainable Water Infrastructure: Towards a Diversified Water Supply”, analyses the efficacy of each of these water sources in the local context of Hong Kong. It starts with the three current water resources of local yield, Dongjiang water and seawater flushing, followed by the proposed taps of recycled water and desalinated water.
Rainwater accounts for approximately 30% of Hong Kong’s total freshwater each year. Around 50% of total annual rainfall lands in the current catchment area, but only about 10% of that total is collected since most rainfall volume is concentrated in a short period of time, making it difficult to collect and store.
~50% of annual rainfall lands in our catchment area, but only ~10% is collected
While the expansion of storage for additional Dongjiang water would be useful, it would also be expensive. A review of the literature surrounding shape modification of large storage reservoirs finds this to be a non-viable option, as the scale and cost of modifications generally have a payback period of over 250 years. Additionally, it would not significantly increase the reliability of supply in the face of climate change, as it does not reduce Hong Kong’s overall dependence on natural flows.
Dongjiang water now accounts for up to 80% of Hong Kong’s total freshwater supply. Since 2006, the Dongjiang water purchase agreement between Hong Kong and Guangdong adopts a “lump sum deal” model, which guarantees Hong Kong 820 million m3 a year, regardless of drought conditions in the Pearl River Delta.
The true cost of Dongjiang water is in fact higher than that listed in the purchase agreement
Of this volume, we typically use about 640 million m3 based on a 10-year average: the full amount was only used in 2011. Hong Kong is required to pay the full amount stipulated in the agreement, regardless of how much water it actually uses, meaning the true cost of the water is in fact higher than that listed in the purchase agreement.
Hong Kong is one of the few coastal cities that maintains a dual-reticulation plumbing system and uses seawater for toilet flushing. For the last 60 years, this system has been integral in ensuring Hong Kong’s water security by offsetting a significant proportion of freshwater use. The economics of its further expansion and future use are, however, less clear.
Studies have found that the two most important factors determining whether seawater flushing is economical are population density and distance from the coast. As Hong Kong continues to develop and its population migrate into less dense areas away from the coast, that would make other alternatives more cost-effective for WSD and attractive to building owners, who would no longer have to worry about seawater corrosion of appliances.
WSD is looking into increasing the network coverage of lower grade water by expanding the use of seawater flushing and recycled water, comprising harvested rainwater, treated grey water and reclaimed water, for non-potable purposes.
1. Harvested rainwater and treated grey water
Harvested rainwater is the rainwater collected from surfaces such as roofs and stored for future use, whereas grey water is the water collected from showers, kitchen sinks and laundry machines etc. that can then be treated for use.
A typical rooftop harvesting system was only able to provide 25% of the water required for washing machines in a high-rise building…
A study carried out in Hong Kong found that a typical rooftop harvesting system was only able to provide 25% of the water required for washing machines in a high-rise building. The amount of space needed to make a system financially viable also make harvesting generally unattractive and potentially impractical for a typical private building in Hong Kong.
…it will be difficult for existing buildings to justify retrofitting without incentives
Even though grey water recycling has a stable water supply within the system, the government has the least control over the installation of these systems due to their small scale and decentralised nature of installation and use. The economics and feasibility of grey water recycling are also site-specific, and it will be difficult for existing buildings to justify retrofitting without incentives.
2. Reclaimed water
Reclaimed water is essentially wastewater that has been treated to standards consistent with local water quality regulations. It is becoming an increasingly common water resource around the globe, particularly for potable use.
Reclaimed water can can compete with freshwater supply alternatives for a range of non-potable uses in nondomestic sectors
While treating reclaimed water to potable standards would not be practical nor economically viable in Hong Kong, it can compete with freshwater supply alternatives for a range of non-potable uses in nondomestic sectors. However, wide-scale implementation will face challenges in both public acceptance and the development of necessary infrastructure and institutional knowledge.
Desalinated water is currently planned to contribute 5% of projected total freshwater demand on a stand-by basis. In spite of its drought-resilient nature, desalination is energy-intensive and potentially environmentally damaging, hence its large-scale use is not advisable in Hong Kong.
Dongjiang water is currently cheaper than desalination & water reclamation can produce high-quality water with less energy & cost
While Hong Kong lacks local water resources, its access to Dongjiang water from Guangdong is currently cheaper than desalination and may remain so under future purchase agreements. Furthermore, water reclamation presents a similarly drought-resilient water source that can produce high-quality water with less energy and at a lower cost. When viewed in this context, it is difficult to support the advocacy by the Legislative Council and WSD for significant investment in desalination.
As reflected in our analysis, summarised in the Water Resource Snapshot, we see that the current plans of WSD are not aggressive or ambitious enough to lower Hong Kong’s reliance on natural flows, nor do they appear to increase the long-term resilience of the system in the face of climate change.
As such, Civic Exchange would like to make the following policy recommendations based on climate resilience, water sustainability, technical feasibility, public acceptance and potential for expansion.
1. Reduce reliance on natural water cycle
As the current Dongjiang water purchase agreement expires in 2020, the Hong Kong government can consider to renegotiate the nature of the agreement to maintain stability of Dongjiang water prices over the years, and set a lower fixed portion with a variable portion available as needed, which could even be charged at a higher price to encourage conservation efforts.
2. Set an ambitious vision for the deployment of reclaimed water in non-potable uses
Currently, WSD plans to deploy just 2.5% of recycled water for non-potable uses. We propose a more ambitious vision of 20% should be set to cover non-potable uses, representing savings of 197 million m3 or the freshwater usage of the entire government establishments and flushing sector.
3. Reconsider the necessary conditions for deploying desalination as a backup option of freshwater supply
Producing our water through desalination has the potential to substantially increase associated electricity demand, particularly once distribution is considered. Further, the potential impacts of desalination on the water supply could be more easily and cheaply met with improved conservation and policy efforts.
Sourcing fresh water using methods that are less energy-intensive & have less impact on the environment than desalination is preferable
Beyond the climate change links, researchers have become increasingly concerned with impacts on marine biodiversity and ecosystems linked to desalination operations. Sourcing fresh water using methods that are less energy-intensive and have less impact on the environment, in conjunction with adherence to strict water conservation measures, is preferable for both economic and environmental reasons in most situations.
Civic Exchange has a long-standing track record on local water issues, and in 2019, they addressed Hong Kong’s inefficient water usage through the lenses of water demand and supply in the two-part Modernising Hong Kong’s Water Management Policy. Read them online now!
Legislative Council Secretariat, Research Brief: Water resources in Hong Kong, June 2015, Hong Kong: HKSAR Government, https://www.legco.gov.hk/researchpublications/english/1415rb05-water-resources-in-hongkong-20150611-e.pdf (accessed November 2018).
Mc Jannet, D., Cook, F. and Burn, S., Evaporation Reduction by Manipulation of Surface Area to Volume Ratios: Overview, Analysis and Effectiveness, 2008, Urban Water Security Research Alliance, http://www.urbanwateralliance.org.au/ publications/UWSRA-tr8.pdf (accessed 7 November 2018).
Dongjiang water figures for these years were obtained from WSD information requests
Gao, X., Kim, Y. and Lee, H.W. (2014), “Life-cycle Cost Analysis of Using Rainwater Harvesting Systems in Hong Kong Residential Buildings,” Journal of the Korean Housing Association, Vol. 25, pp.53-62.
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