[Twenty-four months of external control of fluoride levels in the public water supply in Pelotas, Rio Grande do Sul, Brazil].

The aim of the present study was monthly evaluation of fluoride levels in the public water supply in Pelotas, Rio Grande do Sul State, Brazil, and the validity of forming external control groups. Pelotas was divided into 16 geographic regions, including the three public water treatment stations. Water samples were collected from November 1999 to October 2001. Two samples were drawn from each region. Samples were sent to the Fluoride Health Surveillance Laboratory at Universidade do Vale do Itajaí. Fluoride analysis used an electrometric method (Orion 920 A/Electrometer Orion 9609). After 24 months, 764 samples were collected, demonstrating a discontinuity in the fluoride levels. There was an increase in the number of samples with an ideal concentration of fluoride. However, several points with excessive fluoride levels (> 0.9ppmF) also appeared. Based on these results it was concluded that external control is essential for monitoring fluoride levels in the public water supply.