BEIJING: Concerns are being raised in China over the sharp drop in the quality of tap water in Beijing over the past two years.

Tests have shown that specific contaminant levels are bordering close to unhealthy limits. Many residents are now turning to bottled water.

For the Hou family living in Beijing, tap water - even if boiled - is unfit for drinking.

Like many others in China, they have switched to buying bottled water. Tap water is now used only for washing vegetables and rice.

They are even more cautious because they have a baby in the house now.

Hou Kun, a Beijing resident, said: "I would boil bottled water then cool it for the baby to drink. Tap water is an absolute no for him. Honestly I don't even feel safe using tap water to wash his milk bottle."

There is no official comparison of tap water quality changes available as such details have been long kept secret from the public until only recently, when the government promised to post details of water quality online.

For the past decade, tap water has been tested at a laboratory of the Beijing Healthcare Association. It found an alarming increase in the level of contaminants in tap water over the past two years.

Zhao Fei Hong, president of Beijing Healthcare Association Drinking Healthy Committee, said: "Take the level of nitrite for instance, years ago its index was about one to just over two. In 2011, it became over four. In 2012, it jumped to over nine. The water quality has deteriorated quickly. In previous years it would drop a little but not so drastically."

Nitrite is a contaminant in water which can originate from fertilizers, industrial and municipal discharges.

A concentration of more than nine milligrams per litre borders close to the national limit of 10 milligrams per litre.

The waterworks authorities say tap water is safe for drinking, but experts say that doesn't mean it's good for you.

Chen Zhen Ling, a Beijing resident, said: "The water quality now is definitely worse than before. The taste is different. When you make tea, the colour and texture are different."

With rapid urbanisation, Beijing now has close to 30 million residents - including a large mobile population, putting a strain on the drinking water supply.

Another huge concern is secondary pollution of drinking water.

Contamination is rife due to the city's aging underground pipe network, which was laid in the 1990s.

Even though government budgets are allocated for household wastewater treatment, the lack of supervision and regulation is a problem.

Zhang Baocheng, general manager of Beijing Tri- high Membrane Technology, said: "A project could drag on for three to five years before work starts. There is a lot of talk but not much is done in reality. Even when work is done, output and quality is limited. This is one trait of government projects. The company gets paid as long as it wins the project. But it doesn't matter whether they did the job properly."

With doubts over the quality of tap water, many residents in China have switched to drinking bottled water, which is regarded as the safer alternative until recently.

Fresh criticisms have plagued the Chinese bottled water industry over the lack of a national standard and supervision. That leaves residents here with little choice… adding to the many questions over food safety in China.