Nation's drinking water pipelines contaminated with micro-organisms, say experts
Mainland scientists have identified barely a fraction of dangerous micro-organisms that carry disease and devour water-pipe networks
Large colonies of micro-organisms - some capable of causing serious disease - have been discovered inside pipelines carrying drinking water to homes in most major mainland cities, the South China Morning Post has learned.
Fortunately, most people habitually boil water before drinking, killing off the organisms and reducing the risk of outbreaks. But many foreign visitors are unaware of the issue and often drink from the tap.
Senior government officials and water scientists met last year in Beijing to discuss potable water safety, industry insiders say. One possible solution is to launch a national programme to replace pipes with high-quality ones, made either of steel or plastic with special coatings.
But such an effort would be costly and some experts question whether the central government would commit to the funding, and if replacement is the most efficient solution.
Water safety on the mainland has come under scrutiny following a tap water scare in Lanzhou, Gansu province in April. Benzene, which can cause cancer, was discovered in tap water at levels 20 times higher than national limits. An official investigation found that outdated water ducts were to blame and nine officials were disciplined for their role in the incident.
Professor Guan Yuntao, associated with a laboratory in Shenzhen under the auspices of Tsinghua University, has been carrying out government-funded research on micro-organism in urban water networks for several decades. The organisms together with organic compounds and heavy metals are the main contributors to unsafe drinking water. In some cities, membranes consisting of a variety of species can form on the inside surface of pipes - much like plaque in human arteries - "in a matter of days".
Pieces of these colonies occasionally break off and interrupt the flow of water, but often stay put and "chew" on the pipeline from the inside out.
The organisms release corrosive waste materials that accelerate the ageing of pipes, Guan said. Leaks are a common problem and in some cities, up to half the supply is wasted due to problems with the pipe network.
Scientists also worry about the presence of pathogens, a class of organisms that cause disease.
More than a dozen officially backed research projects in recent years discovered a range of pathogens including Legionella, bacteria that can cause deadly strains of pneumonia, Guan said.
He was not permitted to reveal a full list of "sensitive micro-organisms" that had been uncovered due to risks of creating panic among the public. The testing methods employed could identify only a relatively small number of organisms present in the pipelines. Other pathogens could have gone unnoticed, Guan said.
Another option to improve quality is replacing urban drinking water networks, researchers say. "The water research community and related industries are all excited," said Zhang Lan, deputy director of the water office under the China Centre for Disease Control and Prevention. "Judging by the progress so far, a national pipeline replacement campaign will probably begin in the next five to 10 years and cost more than 10,000 yuan [HK$12,600] per metre."
Replacing Beijing's more than 9,000km of pipeline would cost more than 90 billion yuan. The capital consumed 3.6 billion cubic metres of water last year.
Most pipelines on the mainland are made of cast iron, which makes them vulnerable to chemical erosion resulting from micro-organisms, among other agents.
The new pipelines will be made of either steel or plastic with high-tech coatings to reduce the speed and amount of organism growth.
Professor Liu Jingqing is a specialist in urban water supply at Zhejiang University who leads a government research project on pipeline bio-film. Tackling the issue was difficult, he said, given the many questions that remained unanswered.
"Pathogens have been found in pipelines in every city [on the mainland], but we are still struggling with uncertainties - how to identify them, their distribution, where they come from and at what level they become a public health crisis. Our research is only a few years old," he said.
"We have carried out laboratory simulations, but we find the situation in real pipelines is far more advanced and serious."
A popular method worldwide to suppress the growth of organisms is by adding germicidal chemicals such as chlorine. But the amount needed to be effective on the mainland would be so great that consumers would be scared off by the strong odour.
Liu doubted pipe replacement would solve the problem.
"Germs stay and proliferate in even the most advanced pipelines. So far there is no technology that can create a completely germ-free environment," he said.
"Some countries are using pipelines that are more than a century old, but still provide clean water. Even if all the pipelines in China are replaced, the germs will return sooner or later."