China's tap water was found to contain traces of potentially cancer-causing chemical known as N-nitrosodimethylamine (NDMA), according to a study published this weekend out of Tsinghua University.

Samples were taken in 155 sites of 44 cities across 23 provinces around China. Original sources, finished water from treatment plants, and tap water were include in the study.

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Results found that the NDMA concentrations in China were 3.6 times more than in the United States and even far compared with Western Europe, Fortune reported.

NDMA, which is measured in nanograms per liter (ng/L), is a byproduct of the chlorination process in drinking water. It is considered an "emerging contaminant" alongside other related chemicals called nitrosamines.

On average, NDMA concentrations are 11 ng/L on finished water and 13 ng/L on tap water. However, these figures reached 27 ng/L and 28.5 ng/L in Yangtze River Delta. And these levels, according to Chen Chao, an associated profession at Tsinghua University's School of Environment, pose digestive cancer risk to the residents there.

"The NDMA concentration in drinking water is a pressing issue that demands more research and systematic modifications," Chen said.

China People's Daily reported that the carcinogenic chemical is currently not regulated as a drinking water quality standard in the country. And so far, a maximum level has not been set. The World Health Organization has set a cap on NDMA drinking water at 100 ng/L.

Meanwhile, confirming the link between nitrosamines and cancer, Chen Wanqing, director of the National Central Cancer Registry, emphasized that low levels or contact to the substance will less likely result to cancer.

"The trace found in the water cannot lead to cancer via drinking tap water," he said.

China People's Daily reported that NDMA concentration could be lowered by boiling tap water. Fortune, on the other hand, cited Li Fuxing, head of the Beijing Public Health Drinking Water Institute, saying that neither water purifiers nor boiling is effective on removing the chemicals.

TagsNDMA, N-nitrosodimethylamine, cancer-causing chemical, carcinogenic, tap water, drinking water, NDMA drinking water