It was a habit for pupils in a school in Yunnan province to mix cold river water and rice for lunch, said the school's principal on Tuesday in a response to online criticism.

Last week a micro-blogger named Zhang Yunming posted a series of photos showing students in a primary school in Lijiang, Yunnan province, put tap water into a bowl of rice for lunch. They didn't have any vegetables, as the photos showed.

The posting became a hot topic online. But the micro-blogger as well as the principal named Hai said on Tuesday that Internet users misunderstood the photos because mixing river water with rice is a common eating habit among local students, news portal chengdu.cn reported.

The country's nutrition pilot program, aimed at providing meal subsidies to rural students, was already implemented in the school.

The local education authority said water and food were provided in the school but some students still kept the habit of mixing river water and rice.