Endogenous and exogenous dynamics of urban water quality degradation: Analysis of corrosion mechanisms and organic loading in Kinshasa, Democratic Republic of the Congo

Introduction In many sub-Saharan African cities, aging and intermittently pressurized drinking water distribution networks can compromise water quality beyond the treatment plant. In Kinshasa (Democratic Republic of the Congo [DRC]), hydraulic instability, pipe corrosion, and potential external contamination may alter the physicochemical quality of drinking water during distribution. Purpose This study investigated physicochemical degradation processes occurring within the drinking water distribution networks of the communes of Lemba and Kalamu, with emphasis on free residual chlorine stability, corrosion processes, and potential external contamination. Methods The distribution network was monitored through three grab-sampling campaigns conducted at selected households in the communes of Lemba and Kalamu. A total of 20 water samples were collected from 20 sampling points, including 10 in Lemba (L1–L10) and 10 in Kalamu (K1–K10), distributed along the network. Physicochemical parameters were analyzed using standard methods. Spearman correlation analysis was applied to identify relationships among variables and to infer dominant degradation mechanisms. Results Free residual chlorine (FRC) decreased to 0.10 mg/L at distal points, falling below the World Health Organization’s recommended range (0.2–0.5 mg/L), indicating insufficient disinfectant persistence. Two degradation patterns were identified. In Lemba, an endogenous process was observed, characterized by acidic pH (5.86), iron release (up to 0.15 mg/L) suggesting pipe corrosion, and possible localized nitrification (NO₂⁻ up to 0.028 mg/L). In Kalamu, degradation appeared to be driven primarily by exogenous factors, including high turbidity (7.37 NTU), elevated phosphate concentrations (1.47 mg/L), and a strong correlation with organic matter (r = 0.91), suggesting potential intrusion of urban effluents. Conclusion The drinking water distribution network functions as a reactive biogeochemical system rather than a passive conduit, with corrosion, organic loading, and hydraulic instability contributing to water quality degradation. These findings highlight the need for targeted infrastructure rehabilitation and adaptive chlorination strategies to ensure safe drinking water delivery.