The objective of this study was to evaluate the effects of the transfer of the São Francisco River waters on the quality of the water produced by water treatment plant of Gravatá (WTP-Gravatá) using multivariate statistics. Monthly means of the variables pH, apparent color and turbidity of raw, decanted and treated waters were used, in addition to the volume accumulated by the Epitácio Pessoa reservoir, during the period from January 2016 to December 2017. The arrival of the transposition waters abruptly changed the apparent color and turbidity of the raw water. In spite of that, the treated water presented low variability of the mentioned parameters, indicating that the WTP-Gravatá was able to adapt its treatment. From the factor analysis/principal component analysis (FA/PCA) it was found that changes in reservoir volume alter the apparent color and turbidity of the raw water, requiring interventions in the coagulation/flocculation/decantation stages. The increasing of these parameters in the decanted water overloads the filtration step, raising the apparent color of the treated water. The cluster analysis distinguished the different phases experienced by the Epitácio Pessoa reservoir. The information obtained can help decision making in WTPs, considering changes in reservoir volumes.

  • The water transference from the São Francisco River changed the characteristics of the raw water from Epitácio Pessoa reservoir.

  • Changes in the volume of the reservoir influenced the water treatment performed by WTP-Gravatá.

  • Raw water changes demand an adjustment in the coagulation/flocculation/decantation steps and the filtration step may be overloaded.

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