PETALING JAYA: River pollution caused water treatment plants in Selangor - the country's richest state - to shut down 42 times last year, disrupting supply to thousands of consumers for 2,838 hours.
According to the state's main water concessionaire, Syarikat Bekalan Air Selangor (Syabas), the plants in Sungai Semenyih and Bukit Tampoi had already been shut down six times so far this year.
The most recent was in April when pollution of ammonia and manganese in Sg Semenyih caused the plant's closure. And, supply to 395,427 households in the Petaling, Hulu Langat, Kuala Langat and Sepang districts was cut without notice.
Syabas is unable to issue advance notices to consumers for such unscheduled disruptions.
To counter such pollution, Lembaga Urus Air Selangor (Luas), the agency regulating water resources and rivers in Selangor, introduced a monitoring and mapping system, known as E-Luas.
Luas director Md Khairi Selamat said the system, based on data from water intake points, river flow and land use, acted as an early warning to identify potential locations for pollution at all water catchment areas in the state.
He said a "water catchment team" and the Selangor's committee on management of such areas, chaired by the State Secretary, were also involved in the monitoring.
"Based on our checks, the place with the most potential for pollution is Sg Sembah near Rawang which has an increasing number of residential and industrial areas," he said.
Sg Sembah is one of the tributaries and a sub-catchment area for Sg Selangor, which currently supplies over 60 per cent of raw water in the state.
"The river (Sg Selangor) remains clean, according to the Department of Environment's Water Quality Index, and has improved to a 83.57 reading last year as compared with 83 in 2013," he said.
In 2013, a spillage of used engine oil into a drain flowing into Sg Gong, another of the Sg Selangor's tributaries, caused taps to run dry for millions in the Klang Valley.
It prompted the closure of four water treatment plants along Sg Selangor, which produces 2.67 billion litres of water daily.
Md Khairi said any closure of treatment plants would have to be streamlined by Luas via the state's emergency committee on water sources pollution.
Asked how much time and money would be needed for any clean-up operation, he said it would depend on several factors, including the type of pollution, locations and the length of the river involved.
"For instance, for any oil spill, Luas will use oil booms to prevent the oil from flowing into the water intake point," he said.
He added that contractors would have to be appointed for the clean-up.