The Songjiang district government in Shanghai announced Sunday that it would restore water service to approximately 30,000 residents and office workers in the district by midnight Monday after a toxic chemical spill forced officials to shut off the taps three days ago.

The district government suspended water service to the town of Maogang Friday after a ship loaded with chemicals leaked into a river in the town of Zhujing in Jinshan district the previous day, the Oriental Morning Post reported. Since then, the government has been delivering water to residents' homes in fire engines.

The spill wasn't discovered until residents in both towns reported a strange odor in the air to authorities. The chemicals had spread across six square kilometers of the river, the Shanghai Evening Post reported.

Styrene, one of the chemicals that leaked into the river, can cause cancer, according to a chemical expert from Fudan University who wished to remain anonymous.

At least 23 residents in Jinshan district have been hospitalized because of exposure to the pollution. Five of them remained in the hospital Sunday, the People's Daily reported.

Most of the patients felt lightheaded and suffered sore throats, said Jiang Weilin, vice director of the Jinshan district press department.

The Jinshan district government did not suspend water service in Zhujing, even though it was the site of the spill. "The local water plant is more than 13 kilometers away from where the incident occurred," said Wan Jun, a Jinshan district press officer. "We immediately responded to the spill, so it is now safe for residents to use the water."

Wan said that no styrene remains in the district's water mains, though traces of styrene might be found in the pipes leading to residents' homes. He suggested residents boil their tap water before drinking it.

Despite official assurances, some residents weren't taking chances. "I had to use tap water to bath, but I do not believe it is safe enough to drink," said Liao Changying, a Jinshan district resident.

Authorities had used and salvaged more than 580 tons of hyacinth and other pollutant absorbing materials to clean up the spilled chemicals. It also asked authorities in Zhejiang and Jiangsu provinces to pump 100 million cubic meters of water into the Huangpu River to ensure that its water remains safe.

Both the Jinshan and Songjiang authorities advised residents to let their taps run for at least 15 minutes before using the water.

Four people, including the person in charge of the chemical company, have been detained, police said Saturday night. The company was not authorized to sell chemicals.