[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.