A week after used oil was dumped into the Tram Stream, a Hanoi utility still receives contaminated water, but clean-up efforts are having some impact. 

The Tram Stream, which starts from the Phuc Tien Commune, Ky Son District, Hoa Binh Province, is a freshwater source for the Vinaconex Water Supply Joint Stock Company (Viwasupco), which provides tap water in the entire southwestern part of Hanoi, including Thanh Xuan, Hoang Mai, Cau Giay, Ha Dong and several downtown districts. The water is clear and odorless upstream.

Next to the stream is a path, where a week ago, locals saw a truck dumping used oil. On Tuesday, the stream sections contaminated with oil had been thickly covered with sand, but the smell of burnt oil persisted.

A section of the Tram Stream turned black due to oil contamination.

Black oil at the edge of the stream. This has happened throughout two kilometers from the ravine in Ky Son District to a reservoir of the water supply company in Kim Boi District.

Oil-contaminated stream flows to the Dam Bai Lake, which stores freshwater for Viwasupco.

The water flows from the lake into the company's pump stations.

The company's sewers discharge blackish, pungent wastewater.

"The wastewater is usually discharged in the morning and the afternoon. It flows into a 800-meter stream, then the Dong Bai Lake. A few days ago, the water had turned black all over. Now, it's much clearer and less smelly," said Nguyen Minh Thuan, who lives next to the company's pump stations. However, there has been no explanation for the company dumping its wastewater into its freshwater source.

Viwasupco has deployed trucks and personnel to remove the mud and soil from the contaminated stream sections, putting them in bags and gathering them at a waste collection point. How these bags will be disposed of has not been mentioned.

A cleaned section of the stream has gone from black to muddy.

Water in one of the company's tanks has "become much clearer," said locals.

Authorities have taken water samples for testing, said Truong Quang Hai, deputy head of the Hoa Binh Police Department.

Earlier tests have found that the water, contaminated by used oil, contained high levels of styrene, a substance that is probably carcinogenic.

Hanoi authorities have warned people against using the water from Viwasupco for drinking or cooking.