MANILA: Ninety-one percent of people living in Asia have improved access to clean water, a remarkable achievement over the last two decades in the world's most populous region. But its richest countries and wealthiest citizens likely have better water supplies and governments better prepared for natural disasters.

The assessments made by the Asian Development Bank in a study published Wednesday say countries in the region could be disproportionally affected by the potential impact of climate change if they did not rethink how they manage their water resources. Nearly half of the deaths caused by water-related disasters and 90 percent of people affected by such disasters from 1980 to 2006 lived in Asia, the report said.

Developed nations like Australia, Singapore, New Zealand and Japan top the list of nations best prepared to cope with floods, droughts, hurricanes, storm surges and landslides, while Nepal, Laos, Cambodia, Tajikistan, the Pacific nation of Vanuatu and Bangladesh are the least prepared.

No country in the Asia-Pacific region is a model for its management of water services and resources, according to the Manila-based lending and development institution, whose aim is cutting poverty. Thirty-eight developing countries have low levels of water security or have barely begun to improve, and only 11 have set up infrastructure and management systems.

"While the Asia-Pacific region has become an economic powerhouse, it is alarming that no developing country in the region can be considered 'water-secure,'" said ADB Vice President Bindu Lohani.

Nearly 80 percent of Asia's rivers are in poor health. Urban populations are on the rise and so is pollution, while food and energy needs are putting more pressure on the water resources.

Unless these competing needs are balanced, "water security will remain elusive, undermining development gains and the quality of life for billions of people in the region, especially the poor," said Ravi Narayanan, vice chair of the Asia-Pacific Water Forum governing council.

The good news is that the proportion of the region's population with access to drinking water has increased from 74 percent to 91 percent between 1990 and 2010. Progress has been made in all subregions expect the Pacific, where access remains low at 54 percent.

However, access to reliable tap water supply paints a different picture. Although more than 900 million people gained access to piped water, more than 65 percent of the region's population does not have what should be considered a secure household supply.

Most cities in Asia, which accounts for half of the world's 20 megacities, have extensive infrastructure for domestic water treatment and supply, although piped systems often stop short of individual households, and potable water services are not maintained full-time at the point of delivery, the ADB said.

For instance, some cities in China and South Korea provide round-the-clock water service, but in many other cities tap water is only available for limited hours. In Jakarta, water is available in most areas for about 18 hours each day, and in Chennai, India, water is available for an average of only about four hours each day.

Then there is the question of health. About 88 percent of all diarrhea cases are attributed to lack of adequate access to water and sanitation.

Although the percentage of people with access to improved sanitation rose from 36 percent in 1990 to 58 percent in 2010, 1.74 billion people in Asia and the Pacific continue to live without access to improved sanitation. More than 792 million people still suffer the indignity of practicing open defecation, and more than 631 million of these people live in rural South Asia.

There are bright spots, with Southeast Asia making rapid progress, expanding coverage by 23 percent between 1990 and 2010, and East Asia by 35 percent.

The gap between rich and poor is a big factor when it comes to water access and management, the report said. In South Asia, led by Bangladesh, it is estimated that up to 96 percent the rural rich have access to sanitation, compared to only 2 percent to 4 percent of the rural poor. There has been little progress on improving access to sanitation in the Pacific islands, the ADB said.

"In Asia and the Pacific, the correlation between income and access is unequivocal -the wealthy have better access than the poor to water supply and sanitation. In addition, the disparity is growing, especially in the burgeoning smaller cities across the region," the ADB said.

Differences between richer and poorer communities amount to 96 percent in Nepal and 92 percent in Cambodia, India, and Pakistan, it said.

In India and the Philippines, another study by the U.N. Economic and Social Commission for Asia and the Pacific found that public utilities responsible for providing water and sanitation services "lack capacity in all aspects of sustainability, including effective functioning, financing, and demand responsiveness."