Water particle counter measures the size of particles in water by means of a laser light source directed through the sample and a photoelectric detector that measures the amount of transmitted light. The amount of light blockage is equated to particle size. Particle counters have a sensitivity to suspended particles in the range of 1 to 2,500 microm. The sensors are typically calibrated over a smaller measurement range, with the ranges selected to match the specific size particle of interest. It can detect particle concentrations that are not detectable with turbidimeters.