The announcement came after 28 water samples were tested and none came back positive for unacceptable levels of Indulin AA-86, the Texas Commission on Environmental Quality said in a news release.
Indulin AA-86 is an asphalt emulsifier. It apparently got into the water system through "a third party," Mayor Dan McQueen said.
The restrictions were lifted Sunday in two sections of the city that serve more than 250,000 people. The third section was cleared to begin using water again on Friday.
Seven reports of health symptoms related to use of prohibited water have not been confirmed, the news release said.
The TCEQ and EPA will keep testing water systems over the next few days, according to the statement.
"We're going to continue the sampling process and the city is still in a partnership with TCEQ and with the EPA on evaluating our entire water system," McQueen said.
Corpus Christi is a city of about 300,000 people on the Gulf Coast. Fishing is a part of its economy.
"The available information on Indulin AA-86 suggests that there is not a concern for long term persistence of the substance in aquatic systems, nor is there a concern for bioaccumulation up the food chain," the TCEQ statement said. "Thus, we do not believe there's any risk in consuming seafood from the local estuaries that may be receiving water that is discharged into the estuary from the flushing out of the drinking water system."
Water-use restrictions were imposed Wednesday because of the possible water contamination. In response residents packed stores in search of bottled water, which soon was in short supply.
McQueen said the city received dirty water reports three times in December from a company that officials have not identified. The city investigated each time and determined the problem was not with the water from the city's system.
Wednesday, the city told the company to shut off its water because of concern that some water might have back-flowed into a city water main.
The company doesn't have a device that would prevent the water from flowing back into their mains so there is a risk contaminated water made its way into the city's pipes.
A news release from the city said three to 24 gallons of the Indulin AA-86 possibly entered the city's water after an incident in the Corpus Christi industrial district.
The city has flushed several water mains in the zone because of the risk.
In a statement, Ergon Asphalt & Emulsions Inc, which leases and operates part of Valero Marketing and Supply Co.'s asphalt terminal in Corpus Christi, blamed the problem on a soap solution.
"Ergon is not directly connected to the City's water supply line, but purchases water from Valero through a separate water line within the terminal," read the statement.
"A soap solution, which is comprised of approximately 98% water and 2% Indulin AA-86 and hydrochloric acid, back flowed into the separate water line within the Valero terminal. Ergon uses the soap solution in its asphalt operations.
"When the backflow occurred within the Valero terminal complex, the soap solution would have been diluted with the water in the water line."
Valero said it has fully cooperated with the authorities and is offering further assistance.