American Water Works — among the nation’s biggest water utilities — is restarting systems shut down a week ago after being hacked.

The Camden, New Jersey-based supplier of drinking water and wastewater services to more than 14 million people said it was in the process of “reactivating the systems that were taken offline due to its cybersecurity incident.” 

American Water on Monday disclosed the breach of its computer networks and systems, relaying that it became aware of the unauthorized activity the previous Thursday, or October 3. It responded by shutting down its customer portal and pausing billing. 

“The company’s customer portal, MyWater, is now operational, and all standard billing processes are resuming,” American Water said late Thursday in a news release, adding that customers will not face late charges for the time the service was paused. Water quality was not affected and there is no indication that its water and wastewater facilities were impacted by the incident, it said.

An investigation into the breach continues and additional steps have been taken to increase the security of its system, American Water stated. 

American Water spokesperson Ruben Rodriguez said the company would not elaborate further. 

The company has a market capitalization of $26.7 billion, and describes itself as the largest regulated water and wastewater utility in the U.S., operating in 14 states and on 18 military installations. It manages more than 500 water and wastewater systems in about 1,700 communities in California, Georgia, Hawaii, Illinois, Indiana, Iowa, Kentucky, Maryland, Missouri, New Jersey, Pennsylvania, Tennessee, Virginia and West Virginia, according to its website.

U.S. officials have recently become concerned about alleged work by Chinese intelligence officers to breach critical U.S. infrastructure networks such as water-treatment facilities, and tied a cyberattack targeting U.S. broadband providers to the government in Beijing, the Wall Street Journal reported last week, citing people familiar with the matter.