SINGAPORE Asia's poorer and most populous countries China, India, the Philippines, Vietnam and Indonesia are perceived to be the most polluted, while Singapore, Malaysia and Japan are the cleanest, AFP reported on Sunday.

Pollution, which covers the quality of air and water, noise levels and traffic congestion, has been singled out as the biggest complaint among expatriates living in Asia, according to the latest survey by the Political and Economic Risk Consultancy Ltd. (PERC).

"Air pollution is generally considered to be the biggest single environmental problem in Asia, while traffic congestion is another headache throughout the region," PERC said. "The perception of water and noise pollution is more mixed."

In the survey, PERC asked expatriates living in 12 Asian countries and territories to rate the quality of air and water, noise as well as traffic.

Ratings for each category were averaged into an overall grading scale from zero to 10, where zero was the best and 10 the worst.

India emerged the worst overall with a score of 8.31. It was followed by China with 8.03, Vietnam with 7.63, the Philippines with 7.55, Indonesia with 7.33 and Hong Kong with 7.28.

India's major cities have among the highest levels of sulfur dioxide and nitrogen oxide, PERC said. A fifth of its urban households have no access to safe drinking water, just 23 percent have toilets and only 48 percent have sanitation coverage.

"China has one of Asia's most polluted environments. In terms of water resources, this is not a crisis waiting to happen -- it is already there," PERC said.

Singapore emerged top with a grade of 3.38, beating Japan with 3.63 and Malaysia with 4.50 to become the only three countries with a score better than the average of five.

Thailand had an overall grade of 7.02, South Korea 6.25 and Taiwan 5.84.

The Philippines scored the worst in air quality, with a grade of 8.60 -- getting worse from 7.86 in a similar survey last year. Hong Kong came next with 8.47, China with 8.38 and India with 8.13.

For water quality, Vietnam scored the worst with a 9.0, worsening from 8.30 last year. It was followed by India and China with scores of 8.63 and 8.25, respectively.

China was the worst in terms of noise pollution with 8.13, followed by India and Vietnam tied at 8.00 and Hong Kong at 7.77.

In terms of traffic congestion, expatriates gave the thumbs down to South Korea with a score of 9.0. the Philippines, with 8.60, was seen as worse than Thailand with 7.18 and was neck and neck with India which got 8.50.

"Unfortunately, quite a few countries scored badly for virtually all aspects of the environment. In most cases, these were Asia's poorer, more populous countries," PERC said.

Noting that China and more recently India have been seeing faster economic growth, PERC said such expansion has been carried out without effective environmental programs.

PERC warned that "unless the governments change their policies, environmental bottlenecks to development will intensify sooner or later."

"The problem of pollution is not something that can be swept under the carpet indefinitely. It has real, tangible costs on society," the report added.