A portable multi-channel device for optically testing of a liquid sample includes a controller; and a sample holder with a cylindrical sample compartment and at least two optical channels respectively for measuring turbidity of the sample liquid and for measuring one other optical property of the sample liquid. Each of the optical channels including: a light source placed at one end of the channel, a main detector placed across the sample compartment from the light source, a reference detector for measuring an intensity of light emitted by the light source, and an excitation focusing optic for directing a light emitted by the light source through the sample compartment towards the main detector. Signals from the reference detector of the channel, the main detector of the channel, and another main detector of another channel perpendicular to the channel are processed by the controller to evaluate the turbidity of the liquid sample.