Chinese are accustomed to boiling tap water before drinking it because they think this can make the water clean, but an investigative report publicized Monday casts doubt on that belief.

The water quality of at least 1,000 tap water providers in cities is disqualified, accroding to the Century Weekly. [File photo]

The Century Weekly, a magazine under Caixin Media, reported Monday in its cover story that the water quality of at least 1,000 tap water providers in cities is disqualified, citing Song Lanhe, chief engineer of the Urban Water Quality Monitoring Center under the Ministry of Housing and Urban-Rural Development.

Song gave the comment based on a drinking water survey conducted by the center in 2009, the largest of its kind in more than a decade.

"Among more than 4,000 water plants we surveyed, we found the water provided by over 1,000 plants was disqualified," said Song, who added the quality of urban tap water has not improved much since the survey.

The ministry has so far not released results of the survey. The report said this indicated that the underlying truth might be much uglier.

"I am not authorized to tell you the exact figure (of tap water's qualification rate)," Song said.

The controversial report went further, saying that the figure might be around only 50 percent, but the report failed to name the sources who revealed the information.

Online tweets on the country's leading website portal sina.com.cn on Tuesday criticized the country's inability to provide safe water for its people and many disappointed with and worried about the disqualified tap water that could lead to serious diseases due to high CODmn and untreated remnants of heavy metals in the water.

CODmn is an index used to gauge the amounts of organic compounds in the water.

A netizen nicknamed Meteor Popcorn tweeted that he had known that tap water was directly drinkable in some foreign countries since he was very young, however, tap water in parts of China could cause serious disease because some chemical companies are located along the upper reaches of the country's major rivers such as the Yangtze.

Wang Zhansheng, a Tsinghua University professor, said the accumulation of organic compounds in human bodies could lead to cancer and even mutations at worst. The report said the survey has shown that the disqualified tap water was mainly because of high CODmn.

Meanwhile, incidents of water pollution by heavy metals are not rare in the country in its pursuit for fast industrial and economic growth. On January 15, cadmium contamination was detected on the Longjiang River in south China's Guangxi Zhuang autonomous region after fish died in large numbers. The river is an upstream tributary of the Liujiang River, which runs through Liuzhou, a city with 1.5 million permanent residents.

With China's economic boom over the years, the underlying truth is that many water sources are heavily polluted. The report said that simple water treatment methods used in the past could no longer produce safe drinking water.

As of the end of 2009, 98 percent of the surveyed plants were still treating water with conventional methods including coagulation, sedimentation, filtration, and disinfection, but experts argue these simple steps can not treat heavy metals and organic compounds.

Further, Song said that outdated urban water pipes were also likely to cause new pollution.

"Old piles are easy to corrupt and become encrusted with scale, which will produce microbial bacteria and cause pollution," said Liu Wenjun, a researcher in drinking water safety with Tsinghua.

Experts agree the fundamental solution to addressing water pollution is to clean up water sources, however, they say this is a gigantic task that may need 15 to 20 years to achieve.

Meanwhile, providing safe and clean tap water is paramount at present. Implementing stricter water treatment methods and upgrading urban water pipes are urgently needed.

However, water plants claim doing so will be difficult because they will be extremely costly. At the same time, the government investment is inadequate and the state has control on water prices.

Wang Zhansheng and other scholars estimated the costs would increase by around 20 billion yuan (3.2 billion U.S. dollars) per year for the 4,000 water plants if they chose to upgrade treatment methods and water pipes.

Wang said that the government has the responsibility in addressing the issue and treating water pollution. Song said at least 20 percent to 30 percent of the nation's water plants needed to instantly start deep processing of water to ensure water quality.

Meanwhile, the experts have called for the establishment of an independent water quality monitoring agency, and for timely release of the monitoring data to the public, who at present are ill-informed about the quality of their daily drinking water.