Zheng Zhiqiang, deputy head of a government team tasked with investigating the incident, told China National Radio that the team will look into whether the company delayed its reporting of the contamination.

Zheng said the team found that the company detected levels of benzene in the tap water as early as April 2, although the level of benzene was only slightly above the national limit.

Veolia Water Co said on Monday that the company's detection of benzene in the tap water on April 10 was "pure coincidence" because benzene is an item that the company only tests for every six months.

The company said it was testing the tap water quality in Lanzhou as part of a project with the Ministry of Housing and Urban-Rural Development when it detected the contamination.

The city government has begun a project to retrofit the concrete duct between Veolia's water stations with iron pipelines. The project is expected to be completed in three months.

But the authority's actions have failed to comfort many local residents. On Monday, the Lanzhou Intermediate People's Court rejected a lawsuit filed by five city residents who sought civil damages, a public apology and data from water quality tests over the past year from Lanzhou Veolia.

The court said on its official micro blog that it rejected the lawsuits based on Chinese law. According to China's Civil Procedure Law, the only parties that can file lawsuits are government agencies and related organizations.

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