Sat, Oct 24, 2015 - Page 8 News List

City’s murky waters need clearing

By Chan Shun-kuei 詹順貴

Two months after the devastation brought by Typhoon Soudelor, the turbidity level of the Nanshih River (南勢溪) — Taipei’s main source of tap water — remains stubbornly high. The enduring problem led Taipei Mayor Ko Wen-je (柯文哲) to change direction on the issue. He has announced plans to spend NT$2 billion (US$61.5 million) to connect a pipeline directly to the Feitsui Reservoir (翡翠水庫) to bypass the muddy Nanshih River.

However, the plan would not provide a comprehensive solution to the problem.

In the past, after a typhoon has directly struck northern Taiwan, the turbidity level of the Nanshih River usually falls back to 10 to 50 nephelometric turbidity units (NTU) within a day, so that only a moderate amount of chemical treatment is required to restore water clarity.

However, following Typhoon Soudelor, NTU levels of the river remained several hundred times above normal levels.

When Ko said at the end of last month that the city government, in that month alone, had spent NT$60 million on water purification chemicals, many people were concerned: What effect would the dramatic increase in the use of chemicals have on the health of Taipei residents? For how long would this situation continue? Is it really feasible to convert the Feitsui Reservoir into the main water source for Taipei? If not, how should the city government deal with the problem of worsening water quality in the Nanshih River? And are the landslides upstream the only cause for the murky water?

The questions concern the safety and quality of Taipei’s water sources and require further analysis.

First, the water purification chemicals that Ko talked about came in three main types.

Polyaluminium chloride is a chemical used to coagulate, absorb and precipitate sand, stones and other suspended matter to quickly purify water. Chlorine is then added to kill bacteria and disinfect the water, and finally a precipitant is administered to clear the sediment from the bottom of the reservoir. Because of the continuing high water turbidity, the amount of money spent on purification chemicals in one month has almost reached the amount that was spent for the whole of last year. Therefore, one can estimate that the amount of chemicals used during the purification process has increased by between 10 and 100 times the previously used quantity. However, despite the extra chemicals, the water is still not as clear as it should be.

The city government says that the amount of chemicals contained within Taipei’s drinking water falls within permissible levels.

However, polyaluminum chloride is a corrosive that is harmful to the environment. Also, its aluminum content has been identified as causing dementia. Would long-term consumption of water that contains chemical residues have an impact on health — especially on pregnant women and children?

Second, Ko’s plan to divert water from the Feitsui Reservoir — which lies downstream from Beishih River (北勢溪) — would take seven years to complete.

However, in 2006, the Taipei City Government completed the plans for the fifth phase of the Taipei area water supply strategy, which included a project to construct a second extension to draw water downstream from the reservoir.

Unfortunately, because former Taipei mayor Hau Lung-bin (郝龍斌) used the plan as an opportunity to request NT$3.2 billion from the central government, the project was aborted. Now Ko is seeking to resurrect the plan.

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