This work is concerned with the design, development and operation of a Cavitation Susceptibility Meter based on the use of a venturi tube for the measurement of the content of active cavitation nuclei in water samples. The pressure at the ven-turi throat is determined from the upstream pressure and the local flow velocity without corrections for viscous effects because the flow possesses a lam-inar potential core in all operational conditions. The detection of cavitation and the measurement of the flow velocity are carried out optically. The apparatus comprises a Laser Doppler Velocimeter for the measurement of the flow velocity and the detection of cavitation, a custom-made electronic Signal Processor for real time generation and temporary storage of the data and a computerized system for the final acquistition and reduction of the collected data. The main considerations leading to the present design concept are illustrated and the implementation of the whole system is described. Finally, the results of application of the Cavitation Susceptibility Meter to measurement of the water quality of tap water samples are presented and critically discussed with reference to other similar or alternative methods of cavitation nuclei detection and to the current state of knowledge on cavitation inception.