The Vinaconex Water Supply Joint Stock Company (Viwasupco) said that it has to clean its pipes and reservoirs after its water source was contaminated by used oil recently.
It has not set a date for recommencement of water supply, according to Wednesday statements from water companies that receive supply from Viwasupco to redistribute it to households in Hanoi.
A representative of the Ha Dong Water One-Member Limited Liability Company (Hadowa) said it would put its stations in full throttle to compensate for about 40,000 cubic meters of water now no longer available from Viwasupco every day.
The Viwaco Joint Stock Company, which buys about 200,000 cubic meters of water per day from Viwasupco, said it would use water from reserved sources and send tankers to houses in the affected areas.
Viwasupco provides 300,000 cubic meters per day for the entire southwestern part of Hanoi, including Thanh Xuan, Hoang Mai, Cau Giay, Ha Dong and several downtown districts.
Around half of the capital city's residents depend on it for their clean water demand.
But for a week now, their daily life has been badly disrupted by a burned and pungent smell coming from their tap water.
A truck with a loading capacity of 2.5 tons was seen dumping used oil into a mountain creek in Phu Minh Commune, Ky Son District of Hoa Binh Province, a northwestern neighbor of Hanoi on Tuesday last week, the Vietnam Environment Administration under the Ministry of Natural Resources and Environment said Monday.
The creek is on an upstream section of the Da River, the biggest branch of the Red River, which supplies water to Viwasupco's water tanks.
Tests of the polluted water found high levels of styrene, a substance that is probably carcinogenic.
Hanoi authorities have said that people can use the water for other purposes like washing clothes and bathing, but should not drink or use it for cooking.
The city has demanded that Hoa Binh and local police find the truck and the driver that illegally dumped used oil into the environment, but no further information is available on the culprits.
Tran Duc Thang, deputy director of the Department of Natural Resources and Environment of Hoa Binh Province, said it has ordered Viwasupco to suspend supply until its water is guaranteed safe.