Environmental protection officials yesterday urged local governments to ward off heavy- metal pollution and beef up efforts to ensure the safety of drinking water.

The quality of one-fifth of the country's drinking water sources failed to reach national standards, leaving 90 million people with no access to clean water, Zhang Lijun, vice-minister of environmental protection, told the first national conference on drinking water protection held in Shenyang yesterday.

In urban areas, tap water is supplied by 4,000 centralized drinking water sources, including rivers, lakes, reservoirs and underground reserves.

"The result is based on routine monitoring, which examines only basic pollutants. At these source areas, the concentration of some pollutants, such as coliform bacteria and ammonia nitrogen, is higher than the national standards," Zhang said.

"If we use the 109-indicator evaluation system, which includes tests on the concentration of heavy metals and organic toxins, the result will be worse," he said.

China has been faced with an increasing number of major heavy-metal pollution incidents. Several lead poisoning cases involving thousands of children across the country have sparked protests earlier this year.