Air Selangor said, in a statement Saturday, that work at the Semenyih river treatment plant had been paused for the time being.
"This is the fourth such incident this year that involves a main plant, leading to unscheduled water cuts encompassing large areas," Air Selangor said.
The statement added that the source of the contamination had been traced to a sewage treatment facility in Bandar Mahkota and that it has notified the relevant authorities to take immediate action to stop the contamination.
"Some 372,031 users in the Petaling district, Hulu Langat, Kuala Langat and Sepang will experience unscheduled water cuts due to the contamination.
"A timeframe on when the water treatment plant would be operational again has not been established at this time. It will depend on the level of contamination," it said.
Air Selangor also said that updates will be issued from time to time and action taken to ease the impact of the water cuts. It advised consumers to download the Air Selangor app or visit www.airselangor.com for more information and updates.
See below for a list of affected areas: