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Choa Chu Kang Waterworks expansion could hurt biodiversity, but PUB 'committed' to lessen environmental damage

SINGAPORE — National water agency PUB said it is committed to minimising the damage reconstructing one of Singapore’s oldest water treatment plants will cause to the environment in the Western Catchment Area.
A man carrying out upgrading works at Choa Chu Kang Waterworks in 2019.
A man carrying out upgrading works at Choa Chu Kang Waterworks in 2019.
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  • An environmental consultant has proposed mitigation measures to minimise negative impact on a proposed PUB project
  • Choa Chu Kang Waterworks will undergo reconstruction to replace its ageing infrastructure and the site has to be expanded
  • National water agency PUB is committed to implementing all of the mitigation measures recommended
  • A draft report on the impact study was released on July 4
  • PUB is seeking public feedback on the proposals until Aug 1 

SINGAPORE — National water agency PUB said that it is committed to minimising the environmental damage that would arise from reconstructing one of Singapore’s oldest water treatment plants in the Western Catchment Area.

This is for the Choa Chu Kang Waterworks that now treats 80 million gallons of water from Kranji, Pandan, Tengeh, Sarimbun and Murai reservoirs. The reconstruction is needed to allow it to continue to supply good and safe drinking water in future.

The commitment was made in a statement on Thursday (July 7) by Mr Chew Chee Keong, who is PUB’s director of the water supply (plants) department.

This was in response to queries from TODAY after the agency released a report to the public that stated that the impact of the reconstruction work is expected to be on the “slight to major negative level” if no mitigation plans are put in place.

An environmental impact assessment (EIA) by environmental consultant Tembusu Asia — released on PUB's website on Monday — showed that the impact will be reduced to "moderate to minor" levels if its proposed mitigation measures are adopted. 

Mr Chew said that PUB is committed to implementing all of the mitigation measures proposed in the EIA report, and added that the agency is also “prepared to consider” feedback from the public as well.

However, in the course of executing these measures, it will “add to the overall time and cost of the project”, he added.

When asked for details, PUB said that these have yet to be finalised because it is still seeking feedback on the proposed measures.

Mr Chew said: “PUB is sensitive to the trade-offs when new land located close to areas of ecological significance needs to be acquired.”  

He added that the agency has sought to limit the land used for the project and decided to leave the natural streams out of the plant’s proposed extension as much as possible.

The EIA report found that the extension of the waterworks will affect two nearby freshwater streams.

One stream, lying west of the project boundary, is considered to be of conservation value.

A branch of a natural stream that has conservation value. The stream has temporal discharge with low flow velocity during periods of significant rainfall events.

As it is, Mr Chew said that PUB has addressed some of the concerns highlighted in the report, such as sediment run-off, noise pollution and the loss of habitats, by “proposing more mitigating measures“ based on suggestions and feedback from nature groups.

Key measures include altering the original project size to avoid the stream that has conservation value, as well as introducing more earth control measures to manage sediment run-off from construction activities.

Mr Chew’s replies were in response to TODAY’s questions about its public feedback exercise on the EIA report. It also incorporates feedback received during an engagement session held in March this year with the National Parks Board, Urban Redevelopment Authority and representatives from nature groups.

Members of the public will have until Aug 1 to give their feedback. Thereafter, PUB will incorporate relevant feedback and suggestions into the final EIA report, and will work closely with technical experts and agencies to carry out the mitigation measures recommended in the report.

Should PUB go ahead with the project, construction is slated to start in 2023 and end by 2026. The project was originally expected to start this year.

Choa Chu Kang Waterworks is considered one of Singapore’s oldest water treatment plants and is the only one in the western part of Singapore.

It is located about 500m west of Nanyang Technological University’s School of Biological Sciences, and surrounded by a forest on its southern side and the rest of the Western Catchment Area to its north and west.

It was built in two phases in 1975 and 1981.

An aerial view of Choa Chu Kang Waterworks taken in 2019.

The volume of water it now treats from various reservoirs is equivalent to 145 Olympic-sized swimming pools.

TODAY takes a look at some of the finer details of the key findings from the EIA report.


Due to its age, Mr Chew said it is “paramount that we conduct timely renewal” of the infrastructure to ensure that it can keep supplying safe drinking water for years to come.

Aside from enhancing the plant’s maintenance and operation, PUB said last year that when works are completed, it will also improve the safety and security of the premises.

During the reconstruction process, Mr Chew said that the existing plant must continue water production.

He added that there is not enough space within the existing plant to cater to both the ongoing operations and the construction of new treatment facilities to replace aged structures.

“Additional land is therefore needed to house the new infrastructure.”

The interior of a treatment plant at Choa Chu Kang Waterworks in 2019.

As for what will happen to the old infrastructure once reconstruction works are done, Mr Chew said that it will be decommissioned and demolished, with the land set aside for future water infrastructure.


The EIA report said that the project site will be divided into three main construction work areas: Area 1, 2 and 3.

All construction activities in Area 1 are within the existing waterworks plant and covers about 1.2 hectares.

As for construction activities in Area 2, they will take place within a 3.2ha green-field land parcel south of the existing plant.

Area 3 covers an external sewer that will be about 600m long. It will be constructed outside the boundary of the waterworks plant and connected to a deep tunnel sewerage system chamber off the Pan-Island Expressway and Nanyang Drive.


The forest south of the existing waterworks, which consists of an abandoned plantation and scrubland vegetation, was chosen as the site for Area 2 due to its good soil condition, which would not require further ground treatment or improvement works.

This consequently means that the project will be able to be completed by 2026, the report said.

In contrast, having the construction works in other locations with poor soil conditions could affect the schedule for the project’s completion and result in a prolonged period of disturbance to the surrounding environment.

For instance, the soil condition of an area of land northwest of the existing waterworks, where a sludge lagoon was formerly in use, was found to be soft and in poor quality.

The report said that this would be unsuitable for new building construction and to bury new pipework, which conveys drinking water.

Any soil improvement works will take around two years to complete and will adversely affect the expected completion date of the reconstruction efforts.

If construction of new facilities were in the north, it would require an extra relift pump system to convey the water from the existing plant to the new land parcel since the north plot is on higher ground. This will then incur higher pumping energy and cost.

Similar reasons were given to a site northeast of the existing waterworks.

As for a land parcel to the west, the report said that it will encroach into areas of good forest, freshwater streams and biodiversity, while another land parcel to the east has already been reserved by the Land Transport Authority for the construction of an MRT station on the Jurong Region Line.


A biodiversity survey of the areas surrounding the original waterworks site found at least 307 flora species and 191 fauna species, which include birds, mammals, reptiles, amphibians, various types of insects and aquatic creatures.

Specifically, 100 flora species were in the southern land parcel, out of which 68 are native.

Among the rare plants found within the survey boundary, researchers said that the Helminthostachys zeylanica — a kind of fern that is considered critically endangered and endangered in several Asian countries — was the most notable finding because the one recorded during the study is the first record of its kind in Singapore.

As for animals, the report said that the area consists of several threatened species across all taxonomic groups, including the Straw-headed bulbul, the Sunda pangolin, and a very rare Elf dragonfly known by its scientific name Tetrathemis hyalina.

It added that several species found on the site have specific habitat requirements, such as the locally vulnerable four-ridged toad and puff-faced water snake, and the locally near-threatened masked rough-sided frog, all of which are swamp or stream specialists.

The report also said that although other rare and threatened species were not found during the field surveys, some of these such as the Malayan porcupine and leopard cat are known to be found within the Western Catchment area.

The impact from project activities, including vegetation clearance, increased noise and increased artificial light, may have undesirable effects on biodiversity, especially to species of conservation value found within and around the project site, the report noted.


Several concerns were raised in the EIA report that pertained to impact to flora and fauna, noise and light pollution, and disturbance caused by vibration.

PUB’s proposed mitigation measures include, but are not limited to:

  • Identifying plants of high conservation significance to be transplanted
  • Conducting wildlife shepherding and active relocation of animals before land clearing and the hoarding up the worksite
  • Providing noise barriers to decrease the impact of noise to the surrounding fauna
  • Using quieter construction equipment  
  • Continuously monitoring noise levels to ensure they are within acceptable limits
  • Implementing a lighting management plan with construction works limited to daytime where possible.
  • Using low-vibration equipment where possible


By and large, conservationists who were part of the consultation process with PUB said that the EIA took into consideration feedback from the nature community.

Dr Vilma D’Rozario, the co-director of Singapore Wildcat Action Group, added that as an EIA typically acknowledges wild animals found only during the study, she was “happy to note” the mention of the leopard cat and the Malayan porcupine.

My concern is whether mitigation measures will be implemented as well as they are planned.
Dr Vilma D’Rozario, co-director of Singapore Wildcat Action Group

Dr Shawn Lum, president of the Nature Society (Singapore), noted that the vegetation of the site to be built upon is “far from pristine”.

“It is mostly young regenerating forest and abandoned kampung (village) gardens. In the wider context of the Western Catchment area, removing this area will probably not have immediate impact, especially on the rare wildlife found in the area,” he said.

On the other hand, Dr Lum said any green area of marginal diversity and conservation value today can be rehabilitated and restored to eventually become rich, primary habitat.

“Even modest-sized areas can serve as corridors for the movement of wildlife, so I feel that the loss of green spaces needs to be seen from a wider spatial scale and a longer time scale,” Dr Lum said.  

Dr D’Rozario said that the reconstruction of the Choa Chu Kang Waterworks is just “one of a few other largish developments in the area”, and pointed to the nearby Jurong Region Line of the MRT rail network as one example.

“So, coming all together, this will be a blow to biodiversity. I hope that wildlife that can, will have already moved away,” she said.

Mr Marcus Chua, a mammal researcher for the Lee Kong Chian Natural History Museum at the National University of Singapore, said it is “chilling to note” that the total area of forest that will be lost was not considered in the report, since it is specific to the project.

Among other consequences to wildlife, he said that this will have an impact on the leopard cat population as they are predators that need sizeable, forested areas to find food and survive. Most of the leopard cats, he said, are found in the Western Catchment area, which is known for its rich biodiversity. There are likely to be fewer than 20 on mainland Singapore.

“Furthermore, the overall amount of forest cleared would contribute negatively to climate change, and I would like to see more mitigation on that part in either reforestation in the area or carbon capture or credits,” Mr Chua said.

Even though Dr D’Rozario is heartened by PUB’s commitment to the mitigation measures, she said that the “devil is in the implementation”. 

“My concern is whether mitigation measures will be implemented as well as they are planned.”

The full EIA report is available on PUB's webpage. The feedback form is also online.

Related topics

PUB Choa Chu Kang Waterworks water treatment feedback environment biodiversity

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