A certified lab is one that has been reviewed or inspected by the state or a state-approved certification body to ensure compliance with laws and regulations. These labs undergo on-site visits, proficiency testing, and have quality assurance programs in place. They are required for public water systems to ensure reliable results.

On the other hand, a non-certified lab has not gone through the certification process but may still follow EPA protocols and procedures. While results from non-certified labs can be legitimate, it is generally recommended to use a certified lab to ensure the accuracy and reliability of the results.

The US EPA maintains a list of the agency in each state that handles that state's Safe Drinking Water Act State Laboratory Certification Program.

To find a certified lab in your state, you can contact the agency in charge of the program in your state for a list of certified labs, or visit National Environmental Laboratory Accreditation Management System's webpage and search for a lab in your area.