City officials in Corpus Christi, Texas said they have identified the chemical that prompted a mandated drinking water ban late Wednesday night.

During a news conference Thursday morning, city spokeswoman Kim Womack revealed that about three to 24 gallons of an asphalt emulsifier called Indulin AA86 had made its way into the city’s water supply after back-flow incident that occurred late Wednesday, the Corpus Christi Caller-Times reported.

The announcement came about 12 hours after the city issued a mandated ban on drinking or using tap water.

Water samples were sent to a testing facility in Austin and city officials have been working closely with the Texas Commission on Environmental Quality to ensure the public’s safety. The results are expected back Thursday afternoon.

“Everyone has been extremely helpful. They are on top of it,” State Rep. Todd Hunter told the Caller-Times on Thursday. “I’m encouraging them to be judicial and prudent in getting us as much information as possible.”

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Late Wednesday night, city officials issued a warning mandating residents to use only bottled water for cooking and drinking after an unknown chemical made its way into the water system.

Another spokeswoman for the city, Deanna McQueen, said the leak first came to light Wednesday when workers at the refinery discovered the water coming from its faucets had a sheen.

The city warned that “boiling, freezing, filtering, adding chlorine or other disinfectants, or letting the water stand will not make the water safe.”

“Only bottled water should be used for all drinking, beverage and food preparation (including baby formula and juice), making ice, brushing teeth, washing dishes or clothes, washing hands, and bathing until further notice," the release said.

The warning, which went out at around 10:30 p.m. Wednesday night, prompted a rush on water at grocery stores, where long lines formed with people pushing carts filled with packages of bottled water.

At least two large retailers, H-E-B and Walmart, have contacted their shipping centers to have more water sent to the city.

City Councilman Michael Hunter told the Caller-Times that it's unlikely the chemicals are concentrated enough to do harm, but officials are "taking every precaution that we can."

Hunter said a local company reported that the water coming from faucets at its plant had a sheen, but he did not identify that company or the nature of its business. Hunter described the possible contaminants as two petroleum-based chemicals.

The warning is the latest for a city beset by problems with its drinking water.

In May, officials issued their third boil-water advisory in a year. That notice lasted two weeks and officials at the time said it was largely a precautionary measure taken after nitrogen-rich runoff from rain flowed into the water system, resulting in low chlorine disinfectant levels in the water supply.

Boil-water notices were issued last year because of elevated levels of E. coli and another for low chlorine levels, the Caller-Times previously reported. The notices mirrored two others that were issued in 2007.

There have been no reports of illness or sickness from residents due to the water.

The Associated Press contributed to this report.