Dr Frederick Lee
Fellow, Civic Exchange
Indirect Potable Reuse of Wastewater Is a Promising Option but Overlooked by Hong Kong
We welcome the government’s plan to deploy recycled water as a new water source to diversify Hong Kong’s water supply. One problem of this plan is that the proposed target of supplying recycled water to match only two percent of total demand is a gross under-utilisation of this resource, given its many benefits and promises.
Recycled water refers to wastewater that has been channelled from a home or business to a wastewater treatment facility, where it is treated and reused for other purposes. According to the Development Bureau and Water Supplies Department, recycled water comprises reclaimed water—which is converted from treated sewage effluent; treated grey water —which is used water discharged from baths, lavatory basins and wash basins; and harvested rainwater. At the moment, the government is proposing to supply recycled water for non-potable uses, such as flushing, landscape irrigation, and water features.
Direct potable reuse has been ruled out by the government as an option because it claims that “most people do not accept drinking recycled water”. What is missing in the debate, however, is the role of indirect potable reuse if Hong Kong were to attain long-term water sustainability goals at the local, national and global scale. Indirect potable reuse means that the recycled water is delivered to the consumers indirectly. The recycled water is either blended with other supplies or it sits for a while in a storage facility such as a reservoir, before it is piped into a regular water treatment plant for processing.
We argue that, given current technology, it is technically and financially viable for Hong Kong to aspire to expanding the volume of recycled water, in the long run, to account for at least one-quarter of Hong Kong’s water supply. This estimate is derived from some back-of-the-envelope calculations, taking into consideration the constraints and opportunities associated with the overall configurations of our city’s water supply and wastewater treatment networks. In order to reach this target, it would mean that recycled water should serve, indirectly, both potable and non-potable functions. Doing so would also mean that Hong Kongers would have fulfilled our obligations to some larger national and global water sustainability agendas, such as the UN Sustainable Development Goal on Water (SDG 6).
The first step to adopting recycled water as a significant source of water for our city is a recognition, in principle, by the professional community and the public at large, of its multiple functions and benefits. The second step lies in drawing upon ample international evidence to smash the misconceived notion that recycled water is not suitable for potable purposes. The third step pertains to re-constituting the government’s water policy decision-making matrix, underlying which a consumption-led planning approach needs to be replaced by a sustainability-led planning philosophy.
The reuse of treated wastewater, both directly and indirectly, can provide significant environmental, social and economic benefits. According to OECD research, water reuse can improve the environment by alleviating the pressure on river ecologies by substituting for abstraction. Moreover, compared to alternative sources of water supply such as desalination or water transfer, water reuse often requires lower investment costs and energy, thus contributing to the reduction of greenhouse gas emissions.
Moreover, indirect potable reuse is not new and has been proven to be a reliable, drought proof source of drinking water in the United States, Europe and Singapore. The Upper Occoquan Service Authority, located in the state of Virginia, has been operating an indirect potable reuse system successfully since the 1970s. In California, a Groundwater Replenishment System in Orange County, providing indirect potable reuse function, has been in operation since 2008. In Singapore, recycled water intended for indirect potable reuse has been discharged into local reservoirs since the 2000s.
Furthermore, top policy-makers should assert water sustainability as the preeminent guiding principle in formulating Hong Kong’s long-term water policy. This demands our city’s water agency to break away from its business-as-usual approach, where its only priority has been a continuous expansion of water sources to match an ever-growing demand. Instead, they should rigorously cultivate a strong water conservation ethics among the general public, to reduce overall demand, and tap into all locally available supply options, such as indirect potable reuse, so that Hong Kong could significantly reduce imported water from Dongjiang. As a reduction of imported water will help lessen the adverse impact of abstraction on Dongjiang’s ecology, Hong Kong could claim to be playing a ground-breaking and leading role in contributing to water sustainability goals in southern China.
Photo credit (from top): Drainage Services Department, Cosmo Lo