Hundreds of water-quality tests by the Minnesota Department of Health have been compromised by the failure of a lab analyst to calibrate measurement equipment, according to results of an internal investigation announced Tuesday.

State officials said there is no immediate health risk to people drinking from public water supplies — it’s not even clear whether the inaccurate tests made the water look better or worse — but said they felt compelled to release the findings of the internal review.

“The alleged scientific misconduct introduces an unacceptable margin of error for a small portion of the water testing data our lab generated … for environmental health work,” said Dr. Ed Ehlinger, state health commissioner, in a conference call with reporters.

The tests in question, mostly involving samples of surface water and groundwater, were done on behalf of the department’s Environmental Heath Division and the Minnesota Pollution Control Agency (MPCA) to check for volatile organic compounds or gasoline or diesel products in water supplies.

State officials are reanalyzing the data from 2,200 water samples from 276 communities collected between May 2013 and May 2015. They said the affected samples represent less than 1 percent of the water tested by that lab.

The review will start with water samples from Edina, St. Louis Park, Brooklyn Center, Spring Park and Kasota, because tests in those communities either involved particularly harmful chemicals or the results had been close to warning levels, said Michael Schommer, a Health Department spokesman.

The lab analyst has been placed on “investigational leave,” though officials said it’s unclear why he failed to follow in-house training on proper calibration of testing equipment and on ethical testing procedures.

Most of his work involved groundwater or surface water, but he did analyze some drinking water samples when colleagues were away or on leave, state officials said.

The tests under review also involved water samples around two Superfund environmental cleanup sites — the Lindala Sanitary Landfill in Wright County and a known contaminated groundwater plume in the Baytown Township section of Washington County.

Ehlinger said a top priority is to reanalyze groundwater data from those sites as well as any private property water wells in the two regions.

Results could prompt additional water sampling and testing in those regions.

The lapse is not unprecedented around the country. In 2006, the New York Department of Public Health suspended seven inspectors who failed to conduct quality control checks on devices that measured the acid and chlorine levels of drinking water.

The alleged misconduct by the Minnesota analyst was discovered this spring when a company hired to review the state’s water data noticed an irregularity. Water sample analysis was outsourced to a private firm while state health officials investigated the case.

The state resumed water sample analysis as of June, and put the suspect employee on leave in August pending results of the investigation. Ehlinger declined to provide more details on the worker, other than to say he was a longtime employee.

An MPCA official on Tuesday expressed confidence in the Health Department lab and its efforts to prevent similar errors in the future.

“Our goal is to protect the environment and human health,” said Kirk Koudelka, MPCA assistant commissioner. “To do this, we need to have confidence in the data.”