Unsafe but not uniform: seasonality, land use and waterpan identity drive microbial and physico-chemical water quality risk in multi-use waterpans of semi-arid Kenya

Waterpans are small multi-use waterbodies, yet their water quality dynamics remain poorly understood, particularly under combined influences of seasonality, land use, and local waterbody characteristics. This study assessed 12 waterpans in Narok County during wet and dry seasons, measuring Escherichia coli, nutrients, and physicochemical parameters. Multivariate ordination, PERMANOVA, linear models, and generalized linear mixed models were used to evaluate drivers of water quality variation. E. coli was detected in all waterpans across both seasons, with concentrations exceeding World Health Organization and Kenyan drinking-water guidelines (median: 50.5 CFU/100 mL; range: 9–550 CFU/100 mL), indicating widespread faecal contamination. Dry season conditions were characterized by elevated EC, TDS, nutrients (nitrate, nitrite), chemical oxygen demand, and fluoride, consistent with evapoconcentration under reduced water volumes. In contrast, wet season conditions showed dilution effects and improved dissolved oxygen levels. Waterpan identity explained more variation in overall water quality than land use (21% vs 6.6%), suggesting that local factors such as morphology, hydrological connectivity, and use intensity are stronger determinants of water quality than broad catchment classification. Land-use effects were more pronounced during the dry season, whereas wet season rainfall reduced spatial differences among sites. Additionally, dissolved oxygen was significantly negatively associated with E. coli abundance (β = −0.107, p = 0.012), indicating potential oxygen-linked microbial dynamics. The results demonstrate that microbial and physicochemical risks in semi-arid waterpans are spatially heterogeneous, seasonally amplified, and strongly shaped by site-specific characteristics. These findings highlight the need for targeted, seasonally responsive water quality management strategies in dryland water supply systems.

Keywords:

Waterpans, Escherichia coli, fluorides, seasonality, ASALs, water quality