Evanston’s water quality laboratory has received perfect scores from the Illinois Department of Public Health for its fourth check-up in a row.

The lab achieved a score of zero deviations after state inspectors evaluated the procedures, records and tools the facility used to ensure safe drinking water, the city announced Monday. The city’s water plant met more than 200 criteria to reach the perfect score.

“The effort to generate quality data from this lab is apparent. Congratulations on receiving zero deviations,” the state department wrote in its audit report. The department audits the Evanston water plant every two years to make sure the facility meets safety standards.

The water laboratory, located just north of campus, filters water pumped from Lake Michigan and transfers it to 360,000 customers. Workers add chemicals such as chlorine to disinfect the water and remove unwanted pollutants. The laboratory is staffed by a full-time chemist and a microbiologist, who monitor the filtration process. Every month, employees from the Evanston facility take more than 80 water samples to measure water quality.

“I think it’s great. I think it is typical of the kind of work all public health people do, to make sure we are providing safe water,” city utilities director Dave Stoneback said.

The water plant provides about 40 million gallons of water a day to residents in Evanston and six other North Shore suburbs. The city signed a 40-year contract in 1980 with the Northwest Water Commission to provide water to Arlington Heights, Buffalo Grove, Palatine and Wheeling. It is also in negotiation to sell water to other nearby communities.

“We are a customer of Evanston, and we are glad that Evanston provides excellent quality drinking water,” said John DuRocher, the Northwest Water Commission’s executive director.