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Pollution rate and water quality class are sometimes determined
upon microbiological properties
Rate of
pollution and
water quality
classes
microbiological indices
Total amount of
bacteria,
106 cells/cm3
Amount of
saprophytic
bacteria,
1000 cells/cm3
Ratio between
the total
amount of
bacteria and
saprophytic
bacteria
Very clean, I <0,5 <0,5 <1000
Clean, II 0,5–1,0 0,5–5,0 >1000
Moderately
contaminated,
III
1,1–1,3 5,1–10,0 1000–100
Contaminated,
IV
3,1–5,0 10,1–50,0 <100
Polluted, V 5,1–10,0 5 0,1–100,0 <100
Heavily polluted,
VI
>10,0 >1000 <100