Turbidity, Average Values (NTU)	E. Coli (MPN/100 ml)	Processes and Combinations
Up to 10	10	No treatment necessary
10	100	Only disinfection
100	1000	Slow sand filtration
250	1000	Pretreatment + Slow sand filtration
250	10000	Pretreatment + Slow sand filtration + Disinfection
1000	100000	Two pretreatment methods:
		e.g. sedimentation + coarse filtration or
		coagulation/fluctuation + sedimentation
		Subsequently: slow sand filtration + disinfection
100	2000	Rapid filtration + disinfection
1000	3000	Pretreatment + rapid filtration + disinfection