Microbiological quality of inland and coastal springs: Escherichia coli, other coliforms, and implications for public health

Untreated springs remain important domestic water sources in rural communities, yet their microbial safety and spatial and seasonal variability are insufficiently characterised. This study evaluated concentrations of Escherichia coli and other coliforms in inland and coastal springs within the King Sabata Dalindyebo Local Municipality, South Africa. Ten springs, five inland and five coastal, were sampled on five occasions during both wet and dry seasons, producing 100 water samples. Microorganisms were enumerated by membrane filtration, and concentrations were expressed as colony-forming units per 100 mL (CFU/100 mL). Separate negative binomial generalised linear mixed-effects models were fitted for each microbial indicator, with region and season as fixed effects and spring identity as a random intercept to account for repeated observations. E. coli was detected in all samples at concentrations ranging from 4 to 470 CFU/100 mL. After adjustment for region and repeated observations within springs, expected E. coli concentrations were 38.6% lower during the wet season than during the dry season (incidence rate ratio [IRR] = 0.614, 95% confidence interval [CI]: 0.468–0.805, p < 0.001). The adjusted inland–coastal difference in E. coli was not statistically significant (IRR = 1.346, 95% CI: 0.912–1.987, p = 0.135). Expected other-coliform concentrations were 19.3% lower during the wet season (IRR = 0.807, 95% CI: 0.720–0.905, p < 0.001) and 23.4% higher in inland springs compared with coastal springs (IRR = 1.234, 95% CI: 1.019–1.494, p = 0.031). None of the samples complied with the South African National Standard 241-1:2015 requirement for E. coli to be undetectable in 100 mL of drinking water. The findings demonstrate persistent faecal contamination across the investigated springs, with seasonal variation showing a more consistent association with microbial concentrations than broad inland–coastal classification. Routine microbial monitoring, improved spring protection, and effective household water treatment are required to reduce exposure to E. coli in communities that depend on untreated spring water.