Water security for urban water supply in the face of environmental conditions and source water quality: the case of Guandu Water Treatment Plant, Metropolitan Region of Rio de Janeiro

This paper assesseD the level of water security regarding the water supply in the Western Metropolitan Region of Rio de Janeiro, in terms of quality of water resources at the intake point of the Guandu Water Treatment Plant (WTP), related to the environmental conditions and the quality of the water sources. The main security issues were systemically highlighted, in terms of bulk water quality, in the drainage basin of Guandu WTP, responsible for serving 75% of the metropolitan population (8.5 million people). The study area comprises mainly the Guandu River Basin upstream of the WTP catchment point. An analytical model was used for the qualitative assessment of water security, adapted to the case of Guandu WTP, associated with the stressors: "land use and cover", "degradation of the Permanent Preservation Area", "erosion processes", "environmental accidents", and "polluting load". The impacts on the water quality of the Guandu River were evaluated using the indicators: Water Quality Index; percentage of samples in non-compliance with classification of water bodies; and recordings of emerging pollutants. With results indicating a high risk for most stressors, it was concluded that the level of security for water resources quality of Guandu WTP is low, in terms of bulk water. The problems related to Lagoa do Guandu are particularly the most serious, not only because of chronic pollution that has worsened over the decades, but above all because of the intense acute pollution that caused unprecedent water crises in 2020 and 2021.