The water supply to the city of Harbin in China's north-east is to be restored - five days after it was turned off following a chemical plant explosion.
Tests show that the water is now safe to drink, say local authorities
Running water is due to resume after 1100 local time (1900 GMT) after tests showed the level of chemicals in the Songhua river was below safety levels.
The 80km (50-mile) toxic leak has passed Harbin and is set to reach Russian rivers within two weeks.
China has apologised to its Russian neighbour for the spill.
Beijing has begun an inquiry into the spill caused by an explosion at a petrochemical factory on 13 November.
For the last five days, Harbin's 3.8 million residents have been relying on bottled water and water delivered by lorries.
To quicken the clean-up, water was discharged into the Songhua from nearby reservoirs to dilute the spill while the army installed new filters at Harbin's water plants.
Tests showed levels of nitrobenzene in the river, Harbin's main source of water, had dropped below the official safety limit.
13 November Explosion at petrochemical plant, Jilin city
21 Nov Water to Harbin city cut off; local government cites mains maintenance
22 Nov State media say water could have been contaminated after the blast
23 Nov Authorities admit very high levels of benzene have been found in the water
23 Nov Authorities say 100 tonnes of benzene emptied into the Songhua river
26 Nov China apologises to Russia where the pollution is expected to arrive within two weeks
On Friday, levels had been three times above the safety limit, China's state news agency Xinhua reported.
The toxic leak passed Harbin early on Sunday morning, said Lin Qiang, a spokesman for the provincial environmental protection bureau.
As it flows downstream, it is likely to contaminate Russia's Amur river, which feeds water to more than 500,000 residents of Khabarovsk.
Foreign Minister Li Zhaoxing offered his "profound apologies" to Moscow, Russia's Itar-Tass news agency reported.
The spill was "fraught with enormous damage to the natural environment both of China and Russia", he was quoted as saying.
In Khabarovsk, residents have been urged not to panic while the authorities plan to limit the damage from the approaching spill.
As soon as the presence of benzene is detected, a state of emergency will be introduced in Khabarovsk, Russian TV said.
Cold and hot water supplies will be cut off for at least 40 hours and schools, childcare organisations and restaurants will close.