On June 29, Zhang Yunming posted on his Sina micro blog four pictures of a schoolgirl pouring untreated river water into her school lunch of a bowl of rice.

Zhang was a volunteer at Dongjiang elementary school in Dongshan township, Yongsheng county, Yunnan province.

Zhang said in his blog that he felt really sad about it.

"Besides water and rice, the students have nothing to eat," he said, hoping that people from all walks of life could help children there improve their living conditions.

The pictures prompted huge concern online.

Web users started questioning the "nutritional lunch project", a government-subsidized program that was supposed to ensure better food at schools.

One major concern was the program's budget and whether corruption or embezzlement was at play.

The school and the local education administration, however, said that the case of the girl using the tap water only reflects students' eating habits and has nothing to do with the implementation of the lunch program.

"We will educate the children to not drink tap water," said a spokesman for the county's education bureau.

The official also said that the 3 yuan ($0.49) lunch subsidy for each student, and 4 yuan for those under the poverty line, have been allocated properly, and no embezzlement or corruption has been found.

The project was launched in 2011 to improve the nutrition of rural students, who receive a free lunch at school each day.

More than 30 million students in rural China are now benefiting from the government nutritional lunch program, according to the Ministry of Education.

However, reports of foul play are frequent.

In November, the education department in Hunan province dismissed five officials who were caught giving expired milk to students in the lunch program.

Cheng Fucai, an associate professor and deputy director at Shanghai Academy of Social Sciences' Institute of Youth and Juvenile Studies, said an open procurement and distribution process, as well as independent supervision, is critical.

"The project is a good policy in children's welfare, but we don't have a regulated open process to ensure good implementation," he said. "Therefore, we can only rely on individual reports to expose the program's problems.

"Also third-party supervision is needed," Cheng said, pointing out that the education department has a related interest in the money flow and should not take the responsibility as a supervising body.

Guo Anfei in Yunnan contributed to this story.