Fig 4. Basic risk classification of Thermotolerant Coliforms by HWT method.

Each stacked bar displays TTC concentrations divided into categories based on likely health risk, and the percentage of households in each risk category by HWT method. The WHO’s standard for the microbiological safety of water using TTC as an indicator of fecal contamination is no detectable TTC/100mL [22]. The CCDC’s risk classification also considers TTC samples that are below the detection limit as microbiologically safe [21]. At counts of 1–9 MPN/100mL, if sanitary conditions are decent, drinking water is usually low risk for most people, except young children, the elderly, and the immunocompromised. Data exclude 38 TTC outlier cases (outlier inclusion yielded slightly larger proportions of households in the high risk category).