Though some volatile phenol was detected, the water is still safe, and there is no evidence to show the chemical is from the leak, the city said.
Some 8.68 tons of aniline from a chemical plant in Changzhi, Shanxi Province, leaked into the Zhuozhang River on December 31. The river, which is an upstream tributary of the Zhanghe River, is the main source of the 25-square-kilometer reservoir.
Hours before they resumed using the reservoir, the city released test results of water samples from 22 sites around the reservoir.
Samples collected from four kilometers upstream of the reservoir show the concentration of aniline is five times over the national standard, which allows less than 0.1 milligram per liter.
Handan only received news of the leak from Shanxi five days after it occurred. The city promptly switched to ground water instead of the reservoir.
The city of Anyang, Henan Province, on Monday built a filter dam made of activated carbon on the Huanhe River to prevent the pollutants from flowing into the Xiaonanhai reservoir downstream, when the concentration of aniline was 4.65 milligrams per liter in the river, some 50 kilometers from the reservoir.
Zhang Bao, mayor of Changzhi, where the leak started, apologized for not dealing with the incident in a timely manner, saying the city underestimated its severity.
Leaks should be reported to Shanxi provincial environmental authorities within two hours. The authority was informed days after the spill happened.