Authorities in the eastern Chinese province of Jiangsu shut off the drinking water supply to 680,000 people on Friday after finding "abnormalities" in water quality from China's largest river.
"Owing to abnormalities in Yangtze River water, the water supply to the whole city will be temporarily cut off," the Jinjiang municipal propaganda department said in a statement posted to its official Twitter-like service, Sina Weibo.
"The relevant municipal departments have initiated contingency plans, and are actively putting them into effect," it said.
"At around 10:00 a.m. this morning, the municipal water supply company noticed an unusual taste and ... temporarily shut off the water supply,"
"Tests by the environmental protection bureau have tested alternate water sources from the municipal ecology park and found that they have passed the quality test, and can now be used," it said.
The incident is the latest in a string of water pollution scares across China.
Last month, authorities in the central city of Wuhan launched a probe into the contamination of a major river supplying drinking water to 300,000 people, sending thousands of the Hubei provincial capital's 10.22 million residents rushing to supermarkets to stock up on bottled water.
And residents of the northwestern city of Lanzhou hit out at local authorities for a lack of transparency after levels of the carcinogen benzene were detected in the city's tap water at 20 times the legal limit on April 14.
Earlier this week, Chinese scientists found high concentrations of antibiotics and other medicines in the countries' rivers, according to a report in a top science journal.
River water tested by experts from the East China University of Science and Technology, Tongji and Qinghua universities was found to contain up to 68 types of antibiotics, the Beijing News cited the report as saying on Thursday.
Around 90 types of other medical ingredients were also detected, the report, published in a recent edition of the Chinese Science Bulletin, found.
The substances were found "in higher concentrations than in developed countries," the report said, but didn't specify the concentrations.
Scientists tested surface water for cosmetics and pharmaceuticals, including prescription medicines, antibiotics, anti-inflammatory drugs and sedatives, it said.
Around 70 percent of drugs used in China are antibiotics, while the country produces more than 33,000 tons of personal care products including medicines annually, the report said.
The highest concentrations of personal care products were found in sewage plants, livestock waste water and cropland, with the pharmaceutical industry and hospitals cited as the main sources.
A doctor surnamed Zheng who answered the phone at a major hospital in the southern city of Shenzhen called on the authorities to begin testing drinking water supplies for antibiotics as soon as possible.
"The misuse of antibiotics, including the use of antibiotics in food production, is a public health problem facing China," Zheng said.
"The misuse of antibiotics gives rise to resistance, which means that [diseases] then become untreatable."
Meanwhile, Zhejiang-based environmental activist Chen Faqing said the report was another confirmation of the levels of pollution found in China's waterways.
"A lot of that pollution is in the form of antibiotics and chemicals which can be very harmful to human health," Chen said.
He said farmers of livestock, including fish, typically added antibiotics to feed, which was how it entered the human food and water supply.
"[That way] they will get a better income ... and the fish will grow faster," Chen said.
Wu Lihong, an environmentalist from the eastern province of Jiangsu, said the news showed that air pollution isn't the only pressing environmental issue facing the ruling Chinese Communist Party.
"China has to deal not just with smog, but also pollution of its water and soil," Wu said.
He blamed an entirely corrupt political system for the problem.
"The key lies with the fact that, under such a corrupt system, no one finds a way to shut down these factories that don't manage [pollution] properly," Wu said.
"Talking about it is just hot air," he said. "These factories are pumping out their waste, and the local governments are protecting them."
"No one is thinking about the generations to come; they only think of their own profit."
He said China's environmental legislation, which is exemplary and comprehensive on paper, has little effect in practice.
"These laws are really just a way of bamboozling the public," Wu said.
Chinese consumers are reeling in the wake of a string of public health scandals affecting foodstuffs and medicines in recent years, including melamine-tainted infant formula milk, used "gutter" cooking oil, and tainted vaccines.
Officials have admitted that China is facing a "grave" environmental crisis, with more than half its cities affected by acid rain and one-sixth of its major rivers too polluted to use for watering crops.
Amid growing public anger, Chinese premier Li Keqiang in March declared a "war on pollution," including a raft of measures to tackle the swathes of dirty brown smog that linger over much of northern China for days at a time, breaching international safety guidelines.
In March, China's finance ministry earmarked 21.1 billion yuan (U.S. $3.43 million) for spending on energy conservation and environmental protection in 2014, while 64.9 billion yuan (U.S. $10.55 million) will be allocated to agriculture, forestry and water conservation.
Li described the smog as "nature's red-light warning against inefficient and blind development."
But analysts said complicit officials and the continued persecution of environmental activists will prevent Li's plan from having any real effect.
Reported by Xin Lin for RFA's Mandarin Service, and by Ho Shan for the Cantonese Service. Translated and written in English by Luisetta Mudie.