Chemicals used to douse the flames of an enormous fire in McKeesport may have runoff into the water supply.

MCKEESPORT (KDKA) — Residents in the Lower 10th Ward of McKeesport are being told to not drink any water Saturday morning.

The Municipal Authority of Westmoreland County (MAWC) says the water supply may have been contaminated while firefighters were battling the blaze at the McKeesport Autobody Shop on Rebecca Street.

The warning says that firefighting foam may have been sucked into a fire hydrant during that incident.

About 500 homes in the area are affected by this water advisory.

The county says don’t even attempt to use the water from your faucets — in this case, freezing, boiling and anything else won’t reduce the level of chemicals.

READ MORE: Crews Battle Fire At Auto Body Shop In McKeesport For Hours

They say instead, use bottled water or alternatives for drinking, bathing, hand washing and food — anything you might need water for.

All of this is because the county says unsafe levels of Perfluoroalkyl and polyfluoroalkyl substances (PFAs) and glycol may now be in the water system.

The county says they are testing the water, but MAWC announced Saturday morning that they are flushing the system as a precautionary measure.

“We are changing out the water in the lower 10th ward as a precaution. Our information and expertise indicate that flushing will remove firefighting foam constituents, if present. There’s no reason to wait for test results to flush,” said resident manager Michael F. Kukura.

MAWC says they will let residents know when they can drink the water again, but be sure to stick with KDKA-TV on air and online for the latest updates.