China has conducted investigations and research on the condition of underground water to determine the extent of pollution, a senior official from China's top economic planning agency said Thursday.

"Based on the results we've collected so far, the safety of underground water is generally guaranteed, particularly the safety of drinking water from underground," Du Ying, deputy head of the National Development and Reform Commission (NDRC), said at a press conference.

"But we can't rule out the possibility that the pollution of underground water will worsen," Du told the press on the sidelines of the annual session of the Chinese People's Political Consultative Conference National Committee, the top political advisory body.

He said the pollution of underground water is a problem not only in cities but also in rural areas, and is spreading from shallow aquifers to deeper aquifers.

Many Chinese were infuriated after some chemical plants in east China's Shandong Province were exposed to have illegally discharged toxic water underground directly, thus threatening the safety of underground water.

Du said the State Council, or China's cabinet, together with the local government, has sent out teams to investigate the pollution reports.

"Our investigation into the reported pollution is still under way and no conclusion has been reached," Du said.

To ensure the safety of underground water, the exploitation of underground water must be strictly restricted and related law enforcement activity should also be strengthened, Du said, adding that the government is considering drafting a special law for the protection of underground water.

According to data from the NDRC, about one-fifth of China's water consumption, or about 110 billion cubic meters, comes from underground sources every year.

In northern regions like Beijing and Hebei Province, underground water can account for over half of the water used for agricultural, industrial and residential purposes, Du said.