The Mianyang Water Affairs Group Limited, which is in charge of more than 80 percent of the water supply for the city's urban districts, resumed intake from Fujiang River at around 1 p.m. on Wednesday.
"But water supply won't resume until the intake sample passes official examination," said Zhang Yuchuan, a manager with the group.
Though the swollen Fujiang River has not caused flooding in Chongqing, the municipality, a neighbor of the quake-hit Sichuan, also prepared for the potential water pollution.
The Fujiang River entered the Jialing River, a major water source of Chongqing's urban districts, home to 7 million people, on Wednesday morning at Hechuan County.
Chongqing's environmental protection department has kept a close eye on the water quality and issued monitoring reports every two hours.
"So far, the Jialing River's water quality is okay, but if it is found to be polluted, we will close intakes from Jialing and the water supply will all come from the Yangtze River," said an official with the city's waterworks company, who declined to be named.
Chongqing's urban districts have nine intakes from the Jialing River. Even if they were all closed, the water supply would have been guaranteed to meet the need, said the official.