Corpus Christi, Texas, has lifted a water ban for some parts of the city, while continuing to warn residents in the middle of the city not to use their tap water for any reason.
Officials warned residents on Wednesday night of possible contamination by an industrial chemical, and emphasized that boiling or otherwise treating water did not make it safe to use for drinking or washing.
The chemical in question has been identified, Sara Flores of member station KEDT in Corpus Christi reports.
"City officials suspect that a 'backflow incident' at an industrial property caused an asphalt emulsifier to be injected into the city's water system," Flores says. "In concentrated form, the chemical INDULIN-AA-86 can burn skin and cause respiratory problems."
The Associated Press reports that Corpus Christi officials "believe between three and 24 gallons of the chemical contaminated the water distribution system."
City officials have identified Ergon Asphalt & Emulsions, an asphalt company, as the source of the contamination, according to the Corpus Christi Caller-Times newspaper.
Texas state Rep. Todd Hunter, who represents Corpus Christi, spoke with the Caller-Times about the investigation.
" 'We owe it to the public to get answers in a timely manner,' Hunter told the Caller-Times ... 'We can't just keep floating from one update to the next while we try to figure out the science.'
"Because this type of contamination is rare, state and federal agencies do not have an established testing procedure, so it's unclear how long the testing could take to remove the water use advisory completely, Hunter added."
This incident marks the fourth water advisory in Corpus Christi in the past two years, San Antonio TV news station KSAT reports.
In July 2015, the city had a boil advisory after heavy rain; in September 2015 and May 2016, boil advisories were released due to low chlorine levels.
But this time around, city officials say that even boiling the water doesn't make it safe.