Water quality and health risks in Nzeng-Ayong, Libreville: An analysis of waterborne disease exposure and household WASH practices

Flow diagram summarising the study design, findings, and implications. Left panel (Study Context): urban low-income setting in Nzeng-Ayong, Libreville, Gabon; 949 household surveys and 175 water analyses/laboratory tests. Middle panel (Environmental and Behavioral Risks): chemical exceedances of WHO guidelines for barium (Ba²⁺) and iron (Fe); detection of enteric pathogens (ETEC, EIEC/Shigella, Giardia lamblia, Cryptosporidium spp.); behavioural risk factors including outdoor latrine use, low handwashing frequency, and unsafe water storage; leading to co-occurrence of chemical and microbial contamination with poor WASH conditions. Right panel (Health Impact): multivariate regression results showing improved water storage associated with lower incidence (IRR < 1); sanitation access (latrines/toilets) associated with IRR = 0.87; handwashing before meals associated with IRR = 1.19. Footer note: cross-sectional associations only, no causal inference, reverse causality possible. Access to drinking water is vital for preventing waterborne diseases, especially in rapidly urbanizing areas with limited sanitation infrastructure. This study investigates health risks associated with drinking water quality and household Water, Sanitation, and Hygiene (WASH) practices in Nzeng-Ayong, a densely populated district of Libreville, Gabon, undergoing rapid urban growth and infrastructure strain. A mixed-methods approach combined household surveys (n = 949), physicochemical and microbiological analyses of water samples (35 samples from seven sites, yielding 175 analyses), and interviews with local health authorities. Results show barium and iron concentrations exceeding World Health Organization guidelines in several non-controlled sources, alongside prevalent detection of pathogenic bacteria (Escherichia coli, Shigella) and protozoa (Cryptosporidium spp.). Negative binomial regression identified that improved water storage facilities (IRR = 0.893; p = 0.014) and access to sanitation (IRR = 0.873; p = 0.043) were significantly associated with lower incidence of waterborne diseases. Conversely, handwashing and in-home water treatment showed an unexpected positive association (IRR > 1.0), likely reflecting reverse causality bias where households perceiving higher risk are more diligent. This study supports the case for prioritizingWASH infrastructure investment and regulation of water quality to mitigate the persistent burden of waterborne disease exposure in Nzeng-Ayong.