MICROBIOLOGICAL QUALITY OF THE CLARIMUNDO STREAM WATER, NORTHWEST OF RIO GRANDE DO SUL STATE, BRAZIL

Urban water resources might be depreciated by domestic sewage discharges. Urban water resources might be depreciated by domestic sewage discharges. Considering that some bacterial groups are utilized as water quality indicators, this study evaluated the microbiological water quality of the Clarimundo stream (Cerro Largo county, Rio Grande do Sul State, Brazil) during the four seasons of the year 2016. Total and thermotolerant coliforms were determined through the multiple-tube method and heterotrophic bacteria using plate counts, on waters sampled near the stream spring (P1), before the stream cross the greater population density of the city (P2), and after the urban area (P3). Average densities of total coliforms were 2,715 Most Probable Number (MPN)/100 mL at P1, 6,800 MPN/100 mL at P2, and 166,500 MPN/100 mL at P3. Regarding thermotolerant coliforms, at P1, P2 and P3 the observed average densities were 693, 3,455 and 62,250 MPN/100 mL, respectively. Counts of heterotrophic bacteria were higher at P3, reaching an average of 149,000 Colony Forming Units (CFU)/mL in comparison to averages at P1 (2,960 CFU/mL) and P2 (6,770 CFU/mL). Densities of coliforms and heterotrophic bacteria indicate water contamination with organic matter, including fecal material, originated from anthropic activities. The implementation of efficient systems for sewage collecting and treatment might benefit this stream water quality.