Microbial and chemical hazards in multi-use dryland waterpans: temporal variability, local heterogeneity and implications for drinking-water safety

Waterpans are widely used for domestic water supply, livestock, and other livelihood needs across drylands, yet spatial and temporal controls on their drinking-water quality remain poorly understood. We assessed 12 multi-use waterpans over nine sampling campaigns spanning dry and wet seasons, measured physicochemical variables, evaluated guideline-relevant chemical exposure, and tested for Escherichia coli. Water quality did not differ systematically among the three within-pan sampling positions, supporting analysis at the waterpan level. E. coli was detected in all 82 waterpan visits with microbiological data, indicating pervasive non-compliance with drinking-water standards. Fluoride exceeded 1.5 mg/L in 36 of 58 dry-classified visits and 13 of 48 wet-classified visits, while the combined nitrate-nitrite guideline was exceeded in 24 of 106 visits, 23 of them during dry-classified campaigns. Mean child fluoride hazard quotients exceeded 1 at every waterpan in the dry season. Season was the strongest driver of physicochemical variation: eight of 14 variables (pH, total dissolved solids, conductivity, total phosphorus, nitrate, nitrite, fluoride and chemical oxygen demand) were higher in the dry season. Multivariate water quality differed among individual waterpans, whereas land use was not significant, although only 12 waterpans were available. E. coli varied mainly among sampling occasions and individual visits rather than persistently among waterpans. These findings indicate that drinking-water risk in dryland waterpans is multi-hazard and highly heterogeneous. Management should combine universal microbial protection and point-of-use treatment with targeted fluoride and nitrate-nitrite monitoring, intensified surveillance during low-water periods, and waterpan-specific interventions rather than relying on broad land-use classifications alone.