The quality of water resources in urban areas has undergone degradation due to the discharge of domestic and industrial wastewaters and urbanization among other factors. Despite the legal instruments that aim to preserve water bodies, other mechanisms should be implemented, such as monitoring networks and reporting results. Another challenge is the interpretation of the results that may support decision making on the actions that must be taken to preserve the water quality. In this study, we examined the results of physicochemical and microbiological analyses in a monitoring network that comprised 12 sampling stations. Results were compared with water quality standards established in legislation and calculation of two water quality indexes, the Canadian Council of Ministers of the Environment water quality index (CCME WQI) and the National Sanitation Foundation-Environmental Sanitation Technology Company of the State of São Paulo (Cetesb) WQI. Conclusion is that the comparison with quality threshold limits as defined in the legislation, although complete, prevents the reporting on the overall quality of the water body. Application of the quality index allowed communication and interpretation of the results. Another conclusion is that the Cetesb WQI can indicate the degree of contamination of waters impacted by domestic sewage, while the CCME WQI is an effective tool to assess water resources considering different sources of contamination and current legal aspects.

Water resources in urban areas are often impacted by the intense land use in the cities. The development of a surface water monitoring network is a critical element of water resource sustainable management. The city of Caxias do Sul is the second largest metal mechanic industrial region in Brazil. Industrialization seriously impacts river water quality and is a challenge to public authority supervision. The development of a water monitoring network was the solution public authorities found for the municipality environmental management. The network included 12 stations, monitored over 13 months for 15 physical and chemical water quality parameters. Stations were placed according to maps and satellite images, so as to identify the contributing watershed and land use. Principal component analysis (PCA) was one of the techniques used for data analysis. The first principal component corresponded to the variation of total nitrogen, ammonia, total phosphorus, BOD, COD and electrical conductivity and responded for 76.54% of data variance. The variables that comprised the first component indicated that the main source of water contamination was domestic sewage. The second principal component was composed of chromium, nickel and zinc, suggesting sewage discharge from electroplating industries. The third principal component presented aluminum and iron that are naturally found in local soils. The concentrations of such parameters in each monitoring station