Niu Siwei's sense of unease grows each time he hears his students cough.

After eight months with no rain, the village school where he teaches in Nanhua County of Chuxiong, a Yi ethnic prefecture in the southwestern Yunnan Province, has been using water from a local fish pond for cooking.

The feculent water is sterilized with bleach powder, so the meals for the 192 students, aged 7 to 12, always have a strong smell of the chemical.

"At the beginning, the cook believed the more bleach powder he used, the safer the water would be," said Niu. "Once he put 10 grams in 100 kg of water, amost 10 times the safe amount."

Last week, some thirsty students took a few mouthfuls of unprocessed pond water, and came down with vomiting and diarrhea.

The once-in-a-century drought that has left almost 20 million people thirsty in China's southwestern localities, including Yunnan, Guizhou, Guangxi, Sichuan and Chongqing, has aroused widespread concern.

As a result, donations of drinking water are arriving.

The donated water, however, averages only 600 ml a day for each student, less than half of the daily per capita requirement.

Three times a week, Niu takes his students to fetch water from a pond 1,000 meters from school. "Even the girls carry about their own weight in water, and a two-way trip takes only 15 minutes."

But the pond, too, has little water left.

Chuxiong, one of the poorest areas in China, is not alone.