Tap water supplies have returned to normal in the northwest China city of Yulin, after 100,000 people found the water running black due to manganese dioxide sediment in the pipes.

The sediment was washed through the pipes and discolored the water when the water pressure changed on Saturday morning, said Li Jiaoguo, of Yulin Tap Water Company.

Li said the manganese dioxide sediment was not harmful to humans.

The company opened five sluices on the water grid and discharged 10,000 tons of contaminated water from 9:00 AM to 1:00 PM, while householders discharged another 30,000 tons through their taps.

Half of the city's daily tap water consumption of 30,000 tons come from Hongshixia reservoir, which was rich in manganese.

The Yulin government installed equipment in 2000 to remove manganese from the water, but it found no way to deal with the manganese dioxide sediment that has been inside the pipes for decades.

Yulin, in Shaanxi Province, has a population of 300,000.

Domestic water supplies have been in the spotlight since May, after Taihu, Chaohu and Dianchi lakes were choked by blue-green algae outbreaks, halting water supplies to millions.

(Xinhua News Agency July 25, 2007)