COLUMBUS (WCMH)–An investigation released Thursday by The Guardian found that 33 US cities deliberately tried to conceal potentially dangerous levels of lead in their water.

Columbus is among the cities, as are Boston, Chicago, Detroit, Philadelphia, and Milwaukee.

The UK-based publication says it launched this investigation after the water crisis in Flint, Michigan.

The Guardian combed through “thousands of documents detailing water testing practices over the past decade” and said the cities used testing methods that go against US EPA guidelines. These altered testing methods may lower the amount of lead detected in households.

In 21 cities, including Columbus, water testers were instructed to “pre-flush” pipes before testing for lead

In 7 cities, testers were asked to remove aerators from their spouts before running the water, which can reduce lead content.

In 23 cities, including Columbus, testers were told to run water slowly. This can cause less lead to come out of the pipes.

The Guardian asked 81 of the largest US cities east of the Mississippi for their water-testing documents, and 43 responded.

NBC4 reached out to the city of Columbus for comment. City officials sent us this statement in response:

We have been following OEPA guidance for our sampling protocol. Up until a few months ago they had in their protocol to pre-flush and slowly fill bottles so the City of Columbus was following state guidance. Now that OEPA and USEPA have formally come out and changed the protocol we have removed pre-flushing and slow filling from our sampling protocol.

To read the full report, click here.

Cities named in the investigation

Albany, NY

Augusta, GA

Aurora, IL

Bangor, ME

Boston, MA

Bowling Green, KY

Bridgeport, CT

Buffalo, NY

Charleston, SC

Chicago, IL

Columbus, OH

Croton-on-Hudson, NY

Detroit, MI

Galesburg, IL

Grand Rapids, MI

Greensboro, NC

Jackson, MS

Jersey City, NJ

Lewiston, ME

Miami, FL

Milwaukee, WI

Mount Pleasant, SC

Philadelphia, PA

Portland, ME

Rockford, IL

Sebring, OH

South Burlington, VT

Southaven, MS

Springfield, MA

St. Petersburg, FL

Tampa, FL

Warren, MI

Worcester, MA

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