A measuring element for a water meter assembly is provided. The measuring element may be interchangeably installed within a main case that is permanently situated in-line with a monitored piping system. The measuring element includes a measuring channel, an electronics module, and an acoustic reflector plate. The measuring element has a top wall with multiple ports and a bottom wall with a recess. The electronics module is mounted above the top wall. The electronics module includes one or more pairs of ultrasonic transducers configured to transmit ultrasonic signals through the multiple ports into the measuring channel, and a processor to calculate a flow value based on the transmitted ultrasonic signals from the one or more pairs of ultrasonic transducers. The acoustic reflector plate is mounted in the recess and includes at least one concave reflector that reflects the transmitted ultrasonic signals between the one or more pairs of ultrasonic transducers.