Asia is in the grip of a water crisis that could set back the region's robust economic growth if left unresolved, according to a top Asian Development Bank official.
Arjun Thapan, special adviser to ADB president Harukiko Kuroda on water and infrastructure issues, said governments must start managing the resource better to prevent the problem from worsening.
"We certainly believe that Asia is in the grip of a water crisis and one that is becoming more serious over time," Mr Thapan said on the sidelines of a water and urban planning conference in Singapore.
"We believe that the estimate recently made about Asia having a 40 per cent gap between demand and supply by 2030 is a reasonable estimate."
With 80 per cent of Asia's water used to irrigate agricultural lands, the shortage could have serious implications for food supplies, he warned.
Between 10 and 15 per cent of Asia's water is consumed by industry.
Mr Thapan said that the efficiency of water usage in agriculture and industry has improved by only one percent a year since 1990.
"Unless you radically improve the rate of efficiency of water use both in agriculture and in industry, you are not going to close the gap between demand and supply in 2030."
In China, thermal power generation is the biggest industrial water user, he said, noting that biofuels are also "notoriously water intensive."
Mr Thapan said that if left unresolved, the water crisis "has the potential of slowing down" Asian growth.
To manage water usage well, people should be charged for the volume that they consume, regardless of whether water is managed by a private company or a public entity, said Mr Thapan.
"Water cannot any longer be seen as a free and never-ending natural resource. It is a finite resource," he said.
While Asia's rapidly burgeoning cities are key economic drivers, many are also inefficient water users, and this should prompt government policy makers to implement reforms quickly.
Singapore's National Development Minister Mah Bow Tan said that about 200,000 more people every day move into cities and towns from rural areas.
Every three days, the equivalent of a new city the size of Seattle or Amsterdam emerges, said Mr Mah, adding that by 2050, 70 per cent of the global population will be living in cities, up from 50 per cent currently.
Another problem is the volume of used water in Asia that remains largely untreated, leading to massive pollution of water sources like rivers.
Of the 412 rivers in the Philippines, 50 are biologically dead, he said. Between $2 billion and $2.5 billion is needed to clean up Manila Bay and Pasig River in Manila alone.
In China, India, and the Philippines, among other Asian countries, the total availability of water per person per year has fallen below 1,700 cubic metres - the global threshold for water stress, a situation where water demand exceeds the available amount during a certain period.
About 50 per cent of China's Yellow River is so polluted that it cannot support agriculture, and over 50 per cent of the surface water in the country's Hai river basin is not fit for any use, Mr Thapan said.
"There is time, but again much will depend on how quickly you craft your water transformation agendas and how quickly you are able to implement them," Mr Thapan said.