CORPUS CHRISTI, Texas — The city of Corpus Christi is warning its residents not to use tap water as officials investigate an unknown chemical.

The Caller-Times reported early Thursday that a city news release blames a recent back-flow incident in the industrial district. Officials are telling residents to use only bottled water until the safety of the tap water can be confirmed.

According to the city’s release, “boiling, freezing, filtering, adding chlorine or other disinfectants, or letting the water stand will not make the water safe.”