Spatial Distribution of On-Site Sanitation Facilities and Seasonal Bacteriological Quality of the Honi River, Nyeri County, Kenya

Abstract

This study assessed the spatial distribution and proximity of household on-site sanitation facilities to the Honi River and determined seasonal and spatial variation in the bacteriological and physicochemical water quality of the Honi River. Sixty household sanitation facilities within a 200 m riparian buffer were mapped using a Geographic Information System, and their proximity to the river was determined. Water samples were collected in triplicate from upstream (Rurii), midstream (Mweiga), and downstream (Chaka) sites during the dry (January) and wet (March) seasons and analysed using the American Public Health Association Standard Methods for four bacteriological indicators: Escherichia coli, faecal coliforms, total coliforms, and Shigella. Salmonella and Giardia were also screened for but were not detected. Physicochemical parameters comprising turbidity, pH, biochemical oxygen demand, chemical oxygen demand, total suspended solids, total dissolved solids, electrical conductivity, Nitrate-N, phosphate, and detergents were also investigated. Of the 60 mapped facilities, 40 (66.7%) were located within 100 m of the river; overall, 32 (53.3%) were pit latrines and 28 (46.7%) were septic tanks. Mean Escherichia coli concentration was highest at Mweiga during the dry season (14.00 ± 1.00 CFU/100 mL) but shifted to Chaka during the wet season (6.67 ± 0.58 CFU/100 mL), indicating a site-specific rather than a uniform upstream-to-downstream pattern. Between the dry and wet seasons, catchment-mean turbidity rose from 2.61 to 373.56 NTU, total suspended solids from 17.90 to 369.00 mg/L, and Nitrate-N from 0.16 to 12.20 mg/L, whereas electrical conductivity and total dissolved solids declined, consistent with a dilution effect. Chaka recorded the most severe wet-season deterioration (turbidity ≈ 997 NTU; total suspended solids ≈ 981 mg/L; Nitrate-N 17.43 mg/L; phosphate 7.33 mg/L), with wet-season Nitrate-N at Mweiga and Chaka exceeding the World Health Organization guideline value of 10 mg/L. The findings show that Honi River water quality is spatially heterogeneous and seasonally variable, and that although the proximity of sanitation facilities represents a plausible environmental contamination risk, the available data do not establish a direct causal link. The study provides baseline evidence to support risk-based sanitation siting, riparian protection and seasonally targeted water-quality monitoring in the catchment.