Both plants suspended operations yesterday because of the pollution.

It left more than 300,000 consumers in Selangor without water for the second time in a month after pollution detected in Sungai Gong caused unscheduled water cuts for several days in early September.

Air Selangor CEO Suhaimi Kamaralzaman said that as of 12.30pm today, pollution was still being detected with a reading of eight threshold odour number (TON) near the Bukit Tampoi plant and nine TON near the Sungai Semenyih plant.

Sungai Semenyih is the raw water source for both plants, where TON readings at 7.30am were five near the Bukit Tampoi plant and seven near the Sungai Semenyih plant.

The plants can only operate when the pollution reaches zero TON.

Suhaimi said the water treatment plant in Sungai Batang Benar, Negeri Sembilan, had a high reading of 18 TON but did not provide any previous readings for the plant.

Selangor Menteri Besar Amirudin Shari yesterday said the source of the pollution was detected 30km away from the Sungai Semenyih water treatment plant in Sungai Batang Benar.

Suhaimi said it would take “a long time” for water supply to be fully restored to the 309,605 consumers as the Sungai Semenyih and Bukit Tampoi water treatment plants had not been operational for 20 hours.

The suspension of these two plants has seen Air Selangor unable to produce the daily 602 million litres of water required to supply users to 274 affected areas in the Petaling, Hulu Langat, Kuala Langat and Sepang districts.