"It is very hard to decide if it is toxic or what harm it can cause to humans if the water only meets regional criteria but fails the national one," he said.

"But the national criteria should be safe for everyone."

Authorities in Zhejiang declined to comment on Tuesday. However, in a joint statement released over the weekend, Zhejiang's Quality and Technical Supervision Department and its health department said that the quality standard for bottled water implemented in Zhejiang is the same as, if not stricter than, the national one.

The statement said the Zhejiang standard was drafted in 2002, when the national standard was not in place yet, and the provincial criteria for microorganisms in bottled water are the same as national standard after revision in 2005.

In statements Nongfu Spring made on its official micro blog over the weekend and on Monday, the company insisted its quality indexes in a number of toxic elements are two to 11 times stricter than the national level.

It accused a Beijing newspaper of "being ignorant" for "singling out several indexes in a whole system to generate conclusions on standards" and making groundless attacks.

The company said the recent attacks on its product quality were set in motion by one of its rivals C'estbon Food and Beverage. The Shenzhen-based company denied having made the accusation.