Correlation between turbidity signals and concentration in FNU (Formazin Nephelometric Units) in water is shown. Measurement and dilution was performed automatically in ranges from 4000 FNU to 40 FNU. Linearity was demonstrated in ranges from 4000 FNU to 300 FNU and below 100 FNU. Between 150 FNU and 250 FNU a negative slope alternates to a positive slope due to physical effects based in back scatterd light technology.