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Water Fluoride Laboratory Proficiency Testing Program

Engineering Factsheets

State Community Water System Split-Sample Programs

Operators of community water systems typically test water fluoride content every day. To verify the accuracy of their testing method, they also collect a sample once a month or quarterly, depending on their state requirements, and split the sample into two parts. One part of the sample is tested on-site, and the second part is sent to a state laboratory or accredited laboratory for verification testing. This comparison reveals if the particular laboratory technique is correct, and if the reported results are accurate.
In the Engineering and Administrative Recommendations for Water Fluoridation, CDC recommends that states operate a monthly split-sample program with the water systems in their jurisdictions.

State Laboratory Proficiency Testing Program

All laboratories that measure fluoride should participate in a proficiency testing program to obtain accreditation. Proficiency testing assesses a laboratory’s performance in determining an accurate fluoride measurement against a known standard sample. This is an essential quality assessment methodology that assures water fluoride levels are safe and properly monitored.

There are several references for proficiency testing and accreditation, including:

  • National Environmental Laboratory Accreditation Conference (NELAC) for proficiency testing.
  • A state-implemented certification program based on the Environmental Protection Agency’s (EPA) Manual for the Certification of Laboratories Analyzing Drinking Water.
  • International Organization for Standardization (ISO) Guide 43–1 (1997): Proficiency testing by inter-laboratory comparisons.

CDC Fluoride Proficiency Testing Program

In 1978, the national water fluoridation program was transferred from the EPA to the CDC. At that time, the proficiency testing program was considered to be a CDC responsibility because CDC had the only existing fluoride laboratory proficiency testing program.

CDC’s proficiency testing program operated from 1980–2009. During that period, EPA worked with state environmental management programs to develop criteria for accreditation of environmental laboratories reporting on regulatory compliance. EPA now mandates that all laboratories participate in a state-based proficiency program or obtain accreditation from NELAC. Since having a credentialed proficiency validation for laboratory accuracy as a standard requirement fulfills the function of CDC’s proficiency testing program  it was discontinued in April 2009. Through the new structure mandated by the EPA, state laboratories continue to have reliable, accurate sources for verification testing.