This chapter discusses methods of flow detection followed by a summary of wastewater-related level detection techniques. Flow detection applications in the wastewater treatment industry include the measurement of large flows in partially filled pipes using weirs, flumes, or ultrasonic sensors. When water is flowing in regular pipelines, magnetic flowmeters, venturi tubes, flow nozzles, and pitot tubes are the usual sensors. An increase in the flow rate of the liquid conductors moving through the field increases the instantaneous value of the voltage generated. Most liquids or slurries are adequate electrical conductors to be measured by electromagnetic flowmeters. Magnetic flowmeters are bidirectional. Manufacturers offer converters with output signals for both direct and reverse flows. If the water is dirty, containing solids or sludge, the pressure taps must be protected by clean water purging or by use of chemical seals and the orifice plates should be the segmental or eccentric orifice type.