The recent contamination of tap water in Lanzhou, the capital of Gansu province, has exposed weaknesses in the city's management, especially its failure to supervise Lanzhou Veolia Water Co, the main supplier of water to the city, according to a city government spokesperson.

On Friday, authorities found levels of benzene, a chemical used in making plastics and which is known to cause cancer, that far exceeded national safety limits in the tap water of two districts in Lanzhou. Authorities turned off the supply of water to one district and warned residents not to drink the tap water for the next 24 hours. The contamination affected more than 2 million residents.

The water supply was resumed in all of the city's districts on Monday after test results showed that the level of benzene was below the national limit of 10 micrograms per liter.