At the Hamburg Case Pavilion in the Urban Best Practices Area (UBPA), water functions as an air conditioner by keeping room temperatures at 25 C.

With pipes under the floor and above the ceiling, designers have made the water flow through the entire building to balance carbon emissions and heat.

As the only outdoor pavilion, the Chengdu Case Pavilion - which is called the Living Water Park - attracts not only people but also butterflies and birds. The park is a miniature version of Chengdu's Living Water Park, a system that naturally cleans water from the city's Funan River using water rehabilitation systems.

For the past 12 years, the Chengdu Living Water Park has been processing more than 300 tons of heavily polluted water a day from the Funan River. The park is supported by the city's residents and is known as Chengdu's "green lung". It has also won a number of environmental-protection awards.

"We are proud of the park," said Zhao Yin, a visitor from Chengdu. "In fact, many residents take their children to the park on holidays because kids love the place."

The Living Water Park at the Expo has introduced a small ecosystem to purify river water. Visitors see how the ecosystem transforms polluted water into clean, pure water.

Windmills push pollutants into a pond for anaerobic treatment and then the water flows into some 20 small ponds where various plants absorb pollutants.

The process does not only purify the water but also adds oxygen to it, which nurtures fish and other marine creatures.

The park at the UBPA can process 15,000 kilograms of polluted water a day.

"I think this is a very smart idea to purify water without chemicals," said Wang Xinliang, a visitor from Jiaxing, Zhejiang province.

"Many rivers that run through China's cities need to be purified," said Wang. "I believe this idea can be applied in numerous places outside of the Expo Garden."

In cities where big populations and economic activity are creating a high demand for water, the problem of providing enough water must be solved.

While roads and buildings are developing at a fast pace, rivers and lakes are suffering from contamination and are shrinking in size. The invasion of property development into natural water catchments is a common problem shared by cities around the world.

Osaka, a Japanese city developed alongside a river, offers a solution by incorporating water systems into the urban development and traffic systems. To preserve the natural waterways, urban designers in Osaka built bridge-like highways above the water with high-rise buildings next to the water.

"It saves space and makes a nice view," said Rong Yicheng, a visitor from Guangzhou.

"I would love to go there and have a look at the bridges over the beautiful water."

Many think that Shanghai, with its ever-increasing population and demand for natural resources, could benefit from these examples.

But learning from others may not be enough, said Francisco Nunes Correia, a professor with the department of civil engineering and architecture at the Higher Technical Institute of Portugal, at a conference in the Expo Garden in July.

"Shanghai needs to figure out new solutions to problems in a huge city with large populations," he said. "Practices in other countries and cities are more adaptable in small cities with 1 million or 2 million people."

The task of providing good, safe water for everyone is not only for technicians and designers. It is also an assignment for decision-makers, said Correia.

"The only way to resolve water issues is to understand the problems between uses and try to find solutions by reframing the ways of using water," he said.

"The main challenge lies in finding the balance between uses of water, accommodating requirements and taking all interests into account."