The water supply to Handan, a city in Hebei province, was gradually restored on Sunday after being cut off for half a day in response to fears that it had been polluted by a substance used in making dyes, rubber additives and other materials.

"We've changed the source of water from the Yuecheng reservoir to groundwater and tap water was restored to most families today," Hu Xinchun, chief engineer at Handan Water Supply Co, said on Sunday.

He said residents of the upper floors of tall buildings may have to wait before the water pressure in taps returns to full strength. Hu said people living in those circumstances should try to keep some water in storage.

"But there is no need for panic," he said.

Authorities urged the public to wait until the Zhuozhang River had been tested and found to be safe before they drink out of it or eat fish caught in it.

The contamination came from "an accidental chemical leak" into the upper reaches of the Zhouzhang River in Shanxi province, according to a notice released by the Handan government on Saturday night.

An initial investigation showed that a loose drainage valve at a Tianji Coal Chemical Industry Group site in Shanxi allowed nearly 9 metric tons of aniline to seep into the river, Xinhua News Agency reported on Sunday, while an additional 30 tons of the substance became dammed up in an abandoned reservoir.

Aniline is a clear or slightly yellow liquid that is soluble in water and can easily evaporate or seep through soil into groundwater. People exposed to it may have irritation and congestion in the upper respiratory tract and damage to hemoglobin, a protein that transports oxygen in the blood.

The leak was first discovered on Dec 31, when plant employees noticed during a routine check that aniline was flowing out of a broken pipe. They reported the leak to officials in Changzhi, a city in Shanxi province, who, in turn, warned the provincial government on Saturday.

Shanxi officials immediately reported the leak to Handan and Anyang, Henan province, cities through which the lower reaches of the Zhuozhang River flow.

The Anyang government cut the water supply from the reservoir immediately. That action, though, had no effect on the city's water supply, most of which comes from groundwater.

A Changzhi government statement on Sunday said no deaths have been blamed on the leak and the Zhuozhang River's water quality has been improving.

Zhang Bao, mayor of Changzhi, said on Sunday that three coke dams have been built in the Zhuozhang River to filter out pollution and five monitoring spots were set up to relay data about the river's water quality every two hours, according to Xinhua.

Several officials from the company have been removed from their posts and a further investigation into the accident is under way.

Calls to a press officer at Tianji Coal Chemical Industry Group went unanswered on Sunday.

Although Handan and Anyang authorities released their statements about the contamination several hours after Shanxi reported it, people were asking why Changzhi authorities had failed to issue a warning about the leak immediately after it had been discovered.

Wang Yiping, director of the information office of the Changzhi government, defended the city's measures, saying Changzhi has no need to report such cases to the provincial government if it can control pollution on its own, China News Service reported on Sunday.

"If the authorities had reported the accident on time, we could have stored some water in advance to use to flush the toilet and cook," said Wang Yang, a 25-year-old woman working at a Postal Savings Bank of China branch in Handan.

After the water supply was cut on Saturday night, Handan residents began to quickly buy bottled water, which, along with many other types of drinks, disappeared from supermarket shelves overnight.

"We ordered 1,000 boxes of bottled water today," a saleswoman at the Yangguang supermarket said.

Contact the writers at wangqian@chinadaily.com.cn and peipei@chinadaily.com.cn