The Latest on a warning by the Texas city of Corpus Christi for residents to not use tap water (all times local):

12:15 p.m.

The possible chemical contamination of a Texas city’s water supply has been traced to an asphalt producer on an industrial property where officials say there is no means to stop the leak.

Corpus Christi spokeswoman Kim Womack said at a news conference Thursday that city inspectors did not find a “backflow preventer” on the property. She says the company that owns the property and the one leasing it claim there is one.

Officials say the chemical is an asphalt emulsifier that can burn skin if a person comes into contact with concentrated amounts. Upward of 24 gallons of it may have entered the water supply.

The discovery Wednesday of the leaked chemical has led schools to close and long lines at grocery stores where residents are stocking up on bottled water.

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11 a.m.

City officials say a chemical in Corpus Christi’s water supply was first discovered in water at a refinery in the city, prompting authorities to warn residents to avoid tap water.

City spokeswoman Kim Womack said at a news conference Thursday that the chemical is found in asphalt. Upward of 24 gallons of the chemical may have entered the water supply beginning Wednesday.

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.

Officials initially said two petroleum-based chemicals had contaminated the water supply.

Samples of the water have been sent to a lab in Austin.

It is not yet clear when the water will be safe to use.

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10 a.m.

A Texas Gulf Coast city is warning its 320,000 residents not to use tap water due to concerns that two chemicals may have contaminated the water supply.

Corpus Christi officials said in a statement that a “back-flow incident” in an industrial area Wednesday may have led the chemicals to seep into the water.

The warning prompted a rush on water at grocery stores, where long lines formed with people pushing carts filled with packages of bottled water.

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

Corpus Christi has an aging infrastructure and in May the city issued a boil-water notice that lasted two weeks.

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Information from: Corpus Christi Caller-Times, http://www.caller.com