KUALA LUMPUR - Malaysian police have arrested four suspects linked to the latest water pollution incident that led to the closure of four water treatment plants in Selangor, affecting more than one million households in the Klang Valley.

"Acting on the latest reports of water pollution, the police conducted arrests from midnight to early morning today," said Selangor CID chief Senior Asst Comm Datuk Fadzil Ahmat in a statement on Wednesday (Nov 11), as quoted by The Star daily.

"The arrests were made in Gombak, Damansara and Kelana Jaya. Four individuals, aged between 33 and 43, were arrested.

"Meanwhile, a 33-year-old Bangladeshi man and a local man stockpiled chemical materials at the rented premises. It is believed that chemicals were thrown into a sewage hole and flowed to the polluted area," he said.

The suspects are being held under a seven-day remand for questioning, Malay Mail online news reported.

Selangor and the federal territories of Kuala Lumpur and Putrajaya share the same water resources, including rivers and dams, treatment plants and distribution piping networks.

Pollution affecting a river in Selangor could thus affect water supply to parts of the Klang Valley, that includes Malaysia's capital city of KL, the administrative city of Putrajaya and Selangor districts.

Water company Pengurusan Air Selangor said on Wednesday that the four water treatment plants that were shut down have resumed operations, with water supply expected to be fully restored by Friday (Nov 13).

Police on Wednesday raided a factory in Rawang, Selangor, and found 40 barrels stored there which were said to contain 1,000 litres of chemicals waiting for disposal.

Police and several Selangor ruling-party politicians have voiced out the possibility of efforts to sabotage the state government in the water-supply disruption. Selangor state, which controls the water treatment and distribution for the Klang Valley, just last week approved tougher penalties on water-supply polluters after a spate of incidents in recent months that incurred public anger.

"We won't rule out the possibility that after investigating this locality and the premises where the chemicals were dumped that there could be elements of sabotage," said Gombak district Assistant Commissioner of Police Arifai Tarawe, as quoted by Malay Mail.

The Selangor Water Management Authority said on Tuesday that the source of the pollution might be solvents that were found in Sungai Selangor, a major river whose water is treated before being supplied to the Klang Valley.

The pollution has caused operations of water treatment at four plants to be stopped on Tuesday afternoon, namely the Rantau Panjang and Sungai Selangor's Phase 1,2 and 3 plants.

This led to another round of water-supply cuts to 1,139,008 consumer accounts across the Klang Valley.

The latest water disruption came less than three weeks after the last supply disruption.

There have been 10 unscheduled supply cuts this year alone, with odour pollution responsible for six cases between March and November.