ABSTRACT Knowing the relationship between the total suspended solids concentration (TSS), turbidity in the waters, and that turbidity analysis can be done faster and in less expensive way, this study aimed to obtain mathematical model to estimate the total suspended solids (TSS) concentration from the turbidity values for waters of Doce river basin. For this purpose, it was used the water quality database of the Minas Gerais Institute of Water Management (IGAM). The data were pre-treated using the adjusted boxplot technique followed by adjustment of curves for the different management units and rainfall regime period. It was verified the possibility of a single curve through the dummy variable technique, subsequently. With the results it was observed that the adjusted boxplot technique proved to be useful for environmental data. Linear relationships with R2 values, as a rule, were higher than 0.6, however, it was not possible to develop a single model. It is concluded that the generated models presented good adjustments being able to be used for predicting the concentration of TSS as a function of turbidity. However, each management unit in each period of rainfall regime presents particularities that were reflected in the prediction models.

ABSTRACT The achievement of all the water quality parameters that constitute the water quality indices can be a hamper to their use. The objective of this study was to analyze the viability of using minimum indices to monitor water quality, comparing different methods. For this purpose, the Environmental Company of the State of São Paulo database for the year 2016 of the Tietê/Jacaré and the Tietê/Batalha units was used. Four indices present in the literature were compared with the indices currently practiced in the states of São Paulo and Minas Gerais (“standard indices”). For feasibility analysis, the indices were classified by the “standard indices” methods and compared to them. The minimum indices were significantly correlated with the “standard indices”, from moderate to strong degree. The minimum indices, as a rule, overestimated water quality when compared to the index of the state of Minas Gerais; and underestimated when compared to the index of the state of São Paulo. It is concluded that the minimum indices are useful and practicable tools, with respect to the use of the WQI for management purposes. However, such indices should be evaluated periodically to avoid making mistaken decisions.