An unknown substance found near a water inlet supplying Mudanjiang, the third largest city of northeast China's Heilongjiang Province, has triggered panic among local residents but officials vow the water is safe to drink.

A flaky substance was found blocking the water inlet of the No 4 water plant of the Mudanjiang Water Supply Company at 2?PM last Sunday, reducing the incoming water to 80 percent of the normal volume, revealed a statement posted on the local government's website yesterday.

With the fear of a possible water stoppage, some residents of the city, which has an urban population of 800,000, were crowding the local supermarkets to buy bottled water and began to store tap water at home, reports the Xinhua News Agency.

A man surnamed Lu was quoted by Xinhua as saying: "There are too many people buying water now and the water ordering line is always busy."

It is still unknown what the substance was but local environmental protection officials say they have already sent samples to Harbin, the provincial capital, for an investigation and are anxiously waiting for the results.

"We cannot tell what it is and where it comes from yet," said Liu Guojun, an official from the Mudanjiang Environmental Protection Bureau.

"But the substance would grow when the temperature or quality of the water changed, which shows it is organic," he said.

"We will see what we can do when we know what it is," he said, adding that the substance was not in a large quantity and can be dealt with in other ways, such as salvage.

Another official from the pollution control office of the bureau, who wished to remain anonymous, said that tests found the ammoniate and nitride level in the water was found to be a little higher than the standard level, but had already returned to normal after a series of processing, such as adding chlorine.

He said that a reason is that the Hailang River, which feeds the water inlet, is now in its low water period, which increased the substance's concentration.

An Jiuhai, manager of the water supply company, vows the tap water remains safe for drinking, although it might have a little peculiar smell.

"None of the officials I hear of in the government office building have started storing water," he said.

(China Daily February 22, 2006)