This study aims to use the risk assessment approach FMEA as control and safety methodology of water quality in Belém supply system. During the monitoring period were determined indicators free residual chlorine, turbidity, apparent color, pH, fluoride, total iron, total coliforms and E. coli. Collections and analyzes were performed in 46 points of Belém supplies central zone, including water treatment plants, reservoirs drop in the sectors and in the supply network. Each set of data received descriptive statistical analysis, outlier removal and passed the Kruskal Wallis test to determine significant differences between indicators of different supply sectors. It was found that the 3680 measurements, 706 showed no compliance with potability standards (BRASIL, 2011), of which 582 were in the supply network, 92 on the reservoirs drop in the sectors and 32 at treatment plants. The FMEA methodology was applied to all the analyzed indicators, and the points were divided into three groups: REDE, DRS and ETA’s. For the REDE group were identified 18 points of moderate risk and 18 points high risk. For the DRS group and ETA’s all the points were moderate risk. In this research there was no occurrence of despicable risk and critical. The indicators fluoride, total coliforms and E. coli were the most influential, accounting for approximately 15% in the risk weights. However, fluoride indicator contributes to increase the category of risk, because it showed 100% nonconformities with the fluor standards (BRASIL, 1975) in every point. After the categorization of risk, were prepared two maps, one with points and other with contours, representing the risks related to the quality of water for each one of the studied points. The contoured map was best represented the risk, as it presented more comprehensive information.
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