When 16,000 athletes and officials show up this summer, they will be able to turn the taps and get drinkable water — something few Beijing residents ever have enjoyed.

But to keep those taps flowing for the Olympics, the city is draining surrounding regions, depriving poor farmers of water.

Though the Chinese capital's filthy air makes headlines, water may be its most desperate environmental challenge. Explosive growth combined with a persistent drought mean the city of 17 million people is fast running out of water.

Meanwhile, rainfall has been below average since 1999. The result: Water resources per person are 1/30th of the world average, lower even than Israel.

"To ensure the supply for a short period of time shouldn't be a problem, but to keep the long-term sustainable use of resources is a challenge," said Ma Jun, an environmentalist who has written about China's water issues.

In an attempt to ease the water woes, China has turned to a grand engineering feat. Workers are digging up the countryside south of Beijing for a canal that will bring water from China's longest river, the Yangtze, and its tributaries to the arid north by 2010.

The first part of the project is being accelerated to meet anticipated demand from Olympic visitors. By April, the canal is to begin bringing 80 billion gallons a year — an amount equal to the annual water use of Tucson, Ariz. — from four reservoirs in nearby Hebei province.

"I think one of the things the Olympics is showing is it's desperation time and Beijing has the power," said James Nickum, an expert on Chinese water policy issues at Tokyo Jogakkan College in Japan.

In mountainous Chicheng county, about 70 miles northwest of Beijing, dried-out corn stalks stick out of the windblown earth. Farmers limit themselves to two buckets of water a day from icy wells. They are prohibited from tapping what's left in the local reservoir.

The farmers have been ordered to grow only corn, which requires less water but also fetches a lower price than rice or vegetables.

The government offered about $30 in compensation, but farmers say not everyone received it. Too poor to buy coal, they carry discarded corn stalks home on their backs for fuel to heat their homes.

"For two years we've haven't used water for rice, because it's been given to Beijing," said Yu Zhongxin, 56, of Ciyingzi, a village of small houses deep in the mountains by the Hei river, which feeds Beijing's main reservoir.

"But the individual interest submits to the state interests," he said. "I have no objection. I support it for the success of the 2008 Olympics. China must win!"

Sitting on the northeast edge of the arid north China plain, near no major river and 90 miles from the sea, Beijing has had water problems for more than a millennium. Sui dynasty emperors built one of the world's longest canals in the seventh century to bring rice from the fertile south to the capital.

In recent decades, rapid development, intensive agriculture and wealthier lifestyles have both drawn down and polluted the city's water supply.

"Very few people used toilets in the 1950s, but right now everyone uses toilets, uses showers, uses swimming pools, and fancy buildings use lots of water," said Dai Qing, a former journalist who has become one of China's most prominent environmental campaigners.

The last decade has seen the construction of water-guzzling projects across the city from landscaped gardens and artificial lakes to golf courses and parks, many spurred by the Olympics.

"We don't have water but no one mentions it, all the policy makers never mention that, just develop, develop," Dai said.

The city has spent around $3 billion since it won the Olympic bid in 2001. It has built wastewater treatment plants, moved water-intensive industries out of the city and cut down on pesticide and water use by farms. Near its main reservoir, the Miyun, it has closed polluting factories and relocated 15,000 residents to reduce household pollution.

Nearly all Olympic venues and the Olympic Village will use treated wastewater for heating systems and toilets. Recycled wastewater also will irrigate the Olympic Park, which will include a wooded area and an artificial lake.

But the rowing venue, built on the dried-out Chaobai river bed in Beijing's Shunyi district, will use precious water from the Miyun reservoir. Further, an eight-mile-long underground tunnel will divert water from the Wenyu River to keep the landscape green.

Rapid urban development dried out the Chaobai nine years ago. The groundwater in Shunyi dropped at twice the rate of the rest of Beijing from 2006 to 2007, according to the Ministry of Water Resources.

"From the beginning I was against the Olympics," Dai said. "There is not enough for water for us to hold Olympic Games, but they didn't listen."

Beijing's groundwater, which has fallen 76 feet in the last 50 years, is overexploited, experts warn. And construction has paved over the city, so rain drains away instead of soaking through the earth to replenish the groundwater.

A polluted and damaged ecosystem in turn creates less rain, so more water is needed to irrigate city parks and other greenery, said Wu Jisong, a senior adviser to the Beijing Olympic Games Organizing Committee and former director general of the Department of Water Resources.

Similarly, more recycled wastewater is now needed to feed Beijing's artificial lakes, said John Pan, a director at the Beijing Water Authority.

"We cannot blame nature," he said at a recent conference in Beijing. "We must realize that it is the human activity and destruction that has briefly affected the water circulation so we should find effective ways to solve the problem."

Easier said than done in a developing country focused on economic growth. But time appears to be running out.

Waste, fertilizer and pesticides so contaminated one of Beijing's two main reservoirs, that the city stopped using it for residential water or agriculture in 1997. The other reservoir, the Miyun, is down to one-third the water it had 10 years ago, despite government efforts to cut water use by farms and move industry out of the area.

A local farmer, Zhao Fuyin, said the water once lapped at the bases of the trees around the reservoir.

"It has been a government priority to preserve this area," said Zhao as he watched a couple of donkeys amble along the reservoir's dry slopes. "But the reservoir is just not enough."