The supervision of the cooling water flow rate in power producing equipments of hydro-electric plants has been an issue of concern due to the possibility of clogging up measurement instruments by the used non treated flowing water. Furthermore, for economic reasons, a cheap and reliable instrument must be chosen for each of the many monitoring points. In this work, a non-intrusive device was developed and its performance analized for measuring water flow rate in the 0,7 to 7 m3/h range. The basic operating principle is the variation of the vortex shedding frequency with flow rate. An accelerometer placed outside the pipe wall measures the vortex induced vibration frequency. Several tests showed that the instrument is noise sensitive, which must be filtered to reduce the uncertainty of measurement. The Strouhal number was plotted as a function of the flow Reynolds number, showing an asymptotic trend towards an approximately constant value at high Reynolds numbers. The instrument sharply differenciates between flow and non-flow situations. Presently, a signal conditioning effort is being conducted to reduce the uncertainty of measurement of the flow rate, which is estimated in this dissertation.