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Risk categories of contamination. WHO (2011) has developed a classification and color-code scheme for E. coli colonies per 100 mL water sample which are (i) in conformity with WHO guideline—blue (0/100 mL); (ii) low risk—green (1–< 10/100 mL); (iii) intermediate risk—yellow (10–< 100/100 mL); (iv) high risk—orange (100–< 1000/100 mL); (v) very high risk—red (> 1000/100 mL)
