"A major reason for the unqualified drinking water is that the waterworks' facilities are outdated. More than 95 percent of them were built before the new drinking water standards were formulated," said Du Ying, Vice Chairman of the National Development and Reform Commission (NDRC), China's top economic planner.

Meanwhile, aging water pipes and inadequate management of storage facilities in urban communities are blamed for causing further pollution to the water.

Harsh conditions

But Chen Zhenlou, a professor at the School of Resources and Environmental Science of East China Normal University, said that pollution at the source of the water should receive more blame for the unqualified water than aging water pipes, which he said could only add pollutants during delivering water.

Guanting Reservoir in Beijing is the country's first large reservoir built after 1949. In the late 1980s, the ecosystem of the upper reaches of the reservoir deteriorated rapidly due to the rampant discharge of industrial sewage by nearby factories. In 1997, the reservoir was abandoned as a primary source of water for everyday use.

"Since the late 1980s, chemical and industrial sewage have become the main causes of water pollution," Chen said. "They pollute water very fast and the process to purify such water needs much more time and effort."

Chen revealed that none of the cities in the country have the capacity to completely collect and dispose of sewage. Even Shanghai, which has more advanced infrastructure than many other places in China, can only collect and dispose of 90 percent of sewage.

Though chemical elements have been included in water-quality tests, there are many other organic pollutants not covered. "These pollutants have potentially negative long-term effects to people's health," said Zheng Binghui, Vice President of the China Academy of Environmental Science.

In 2005, the State Environmental Protection Administration, the predecessor of MOEP, monitored 206 water sources in 56 cities and found 132 kinds of organic pollutants.

"Compared to ordinary pollutants, organic pollutants are more harmful though their negative effects are not obvious in the short term," Zheng said.

Scandals involving contamination of water by heavy metals have also repeatedly occurred in recent years.

In July 2011, residue from the Xichuan Minjiang Electrolytic Manganese Plant in Aba Tibetan and Qiang Autonomous Prefecture in southwest China's Sichuan Province was washed into rivers by heavy rain, contaminating the Fujiang River, the main source of tap water for local residents.

Luliang Chemical Industry Co. Ltd. in Yunnan Province, which is adjacent to Sichuan, is one of Asia's largest producers of chromium sulfate, a chemical leather tanning agent. Last August, the company was found to have dumped 5,000 tons of toxic chromium tailings near the Chachong Reservoir in Yuezhen Town, as well as in the hills near Qujing City. The resulting water pollution killed fish and livestock and endangered the drinking water of tens of millions of people.

Chromium is a heavy metal that can be found in surface water. It can be absorbed by humans through inhalation, digestion and skin contact. In the 1990s, China started to clean up the chromium industry, and many companies closed or merged. By 2005, only 25 were left, and the State Council, China's cabinet, ordered that all leftover tailings be safely dealt with by 2010. But Luliang Chemical's scandal showed that large quantities of tailings were yet to be treated and dangerous dumping continued after the deadline.

Dong Rubin, a micro-blogger who first exposed the scandal, told the media that hexavalent chromium levels at the dumping sites were 2,000 times the official limit. Hexavalent chromium is the most toxic form of the heavy metal. Contaminated water was flowing directly into the Nanpan River, a tributary of the Pearl River, which supplies drinking water to millions of people in south China.

In January 2012, a 300-km section of Longjiang River in southwestern Guangxi Zhuang Autonomous Region was contaminated by 20 tons of cadmium from the Hongquan Lithopone Factory, which brought concentrations of cadmium in the river to more than five times the official limit of 0.005 milligrams per liter of water.

According to a document jointly released in May 2012 by the NDRC and the Ministry of Housing and Urban-Rural Development, China plans to invest 410 billion yuan ($64.42 billion) before the end of 2015 to upgrade and construct urban water-treatment facilities in a bid to ensure water quality.

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