A chemical spill polluted a reservoir providing drinking water to about 100,000 people in northwest Shaanxi province , but water quality was back to normal yesterday, a local official said. The spill occurred on Friday night when a tanker carrying 25 tonnes of liquid caustic soda skidded in wet conditions into the upper stream of the Xuefeng Reservoir in Hancheng , the city's Environmental Protection Bureau said. The driver was killed and a passenger seriously burned in the accident. The reservoir is a key source of drinking water for Hancheng, serving some 100,000 residents, the bureau said. The local government suspended use of water from the reservoir and supplied water from wells after the spill, Xinhua said. City government spokesman Chang Xiaoping said yesterday the reservoir's water quality had returned to normal yesterday morning after clean-up efforts and normal water supplies would be resumed 'in one or two days'. But Mr Chang also said the water would have been safe to drink even if no clean-up measures had been taken, because the quantity of the pollutant in the reservoir - which stores more than 14 million cubic metres of water - was 'very small'.