Water treatment plants along the Johor River resumed operations late on Sunday after ammonia levels subsided, including Singapore's Johor River Waterworks that had shut down last Saturday morning.
National water agency PUB, which runs the plant, said it had "progressively resumed water supply to both Singapore and Johor" after water quality was deemed suitable for treatment following high levels of ammonia detected in the river last Friday night.
"PUB will continue to monitor the raw water quality in the Johor River closely, to ensure that the water remains suitable for our abstraction and treatment," it said in a statement yesterday.
The state government shut down a chicken farm and a factory producing fertiliser from droppings after identifying both, located near the river, as the source of the pollution.
Malaysia's Environment Ministry called for further action yesterday, including permanently shutting down the businesses, after water supply was cut for 1.8 million users.
Natural Resources and Environment Minister Wan Junaidi Tuanku Jaafar said the operators of the farm and factory should be blacklisted "in order to prevent them from forming other companies which will potentially cause harm to people and the environment".
He called for the local authorities in the area, such as the Kulai Municipal Council, Kulai Land and District Office and Veterinary Services Department, "to look into this matter seriously and expeditiously in order to prosecute the chicken farm owners... to the full extent of existing laws and enforce based on their jurisdiction".
While the farm and factory could face action for breaking environmental laws, licensing of chicken farms falls under the Veterinary Services Department, while permission to operate businesses falls under the local council.
Johor Veterinary Services Department director Aida Muhid told The Straits Times that the farm was licensed, but there are no current regulations governing fertiliser factories. The plant was not registered with the local authorities.
Datuk Seri Wan Junaidi said the Department of Environment had ordered the farm to relocate away from the Johor River in July last year as it was polluting the water, but it did not heed the directive.
"It is also sad to note that fertiliser farms are not regulated as of yet. We are given to understand that the Ministry of Agriculture is currently drafting such laws to regulate fertiliser farms," he added.
Johor State Minister for Public Works Hasni Mohammad told The Straits Times yesterday that water treatment plants in Johor were operating at 50 per cent capacity on Sunday and could be back to full service yesterday, if ammonia levels subsided to normal as expected.
Although the state's water supply company, SAJ Ranhill, said late on Sunday that two of three plants were operational and water supply would be restored by midnight, some people have yet to see water flowing from their taps.
Datuk Hasni explained that it could take up to 48 hours for treated water to reach the taps of affected consumers.