Studies about the hydrodynamic behavior in the lower Amazon River remain scarce, despite their relevance and complexity, and the Water Residence Time (Rt) of this Amazonian estuary remains poorly unknown. Therefore, the present study aims to numerically simulate three seasonal Rt scenarios based on a calibrated hydrodynamic numerical model (SisbaHiA) applied to a representative stretch of the lower Amazon River. The following methodological steps were performed: (a) establishing experimental water flow in natural channels; (b) statistically test numerical predictions (tidal range cycles for different hydrologic periods); and (c) simulating velocity fields and water discharge associated with Rt numerical outputs of the hydrodynamic model varied from 14 ≤ Rt ≤ 22 days among different seasonal periods. This change has shown the significant influence of hydrologic period and geomorphological features on Rt. Rt, in its turn, has shown significant spatial heterogeneity, depending on location and stretch of the channels. Comparative analyses between simulated and experimental parameters evidenced statistical correlations higher than 0.9. We conclude that the generated Rt scenarios were consistent with other similar studies in the literature. Therefore, they depicted the applicability of the hydrodynamics to the conservation of the Amazonian aquatic ecosystem, as well as its relevance for biochemical and pollutant dispersion studies, which still remain scarce in the literature.

Objective: This study aimed to assess the feasibility of using rainwater for human consumption as an alternative water supply in the Eastern Amazon, through a social technology for collection and treatment. Theoretical Framework: Despite the region's water abundance, access to potable water is limited, especially in isolated communities. Rainwater harvesting emerges as a viable alternative, provided its quality is rigorously evaluated. Method: The research was conducted in seven households on Ilha das Onças (Barcarena-PA) and one control unit in Belém. Water samples collected from rooftops and stored in cisterns were analyzed before and after treatment with sodium hypochlorite and filtration using activated carbon and polypropylene candles. Physical-chemical parameters (pH and electrical conductivity) were evaluated and compared with commercial brands, while microbiological parameters (coliforms) and trace metals were also analyzed. Results and Discussion: Rainwater had an average pH of 5.16 and conductivity of 9.1 μS·cm⁻¹; after treatment, these values slightly increased but remained below those found in commercial waters. Treatment reduced the microbiological load, although 53.8% of samples still showed total coliforms and 20.5% E. coli. In general, the samples did not show metal concentrations above the levels established by legislation. Research Implications: The results suggest that, with proper operation and maintenance, rainwater harvesting and treatment systems are a viable solution for water supply in Amazonian communities. Originality/Value: The study highlights a low-cost, sustainable alternative adapted to the region’s socio-environmental context for promoting health and well-being.