These mechanical water flow meters work by measuring the speed of flowing water running through the pipe that causes a turbine or piston to rotate. The volumetric flow rate of the water is proportional to the rotational speed of the blades.
A flow meter (or flow sensor) is an instrument used to measure linear, nonlinear, mass or volumetric flow rate of a liquid or a gas.
The majority of Vortex flow meters cost $1,000 to $3,000. Accuracies are typically in the range of 0.5% to 1.0% of reading.