Groundwater resources are increasingly stressed due to the introduction of contaminants, increased heat pollution when groundwater is used for cooling from data centers and associated electrical generation, as well as high rates of water abstraction for production of microprocessors. Widely deployable flow sensors are needed to understand these complex and novel changes to groundwater hydrology. Existing groundwater flow measurement devices exist, but these instruments are far too expensive to be widely deployed and typically only deliver flow velocity in two dimensions. Furthermore, these devices were designed decades ago and thus lack the software and telemetry capabilities needed for widespread autonomous deployment. We have developed a groundwater flow sensor that addresses these shortcomings and is also able to measure 3-D groundwater flow. We have updated an existing methodology wherein the rate of the movement of a heat plume generated by the device is tracked by individual temperature sensors. We use modern manufacturing techniques and an open-source microcontroller platform known as RRIV to develop and prototype this sensor at a fraction of the cost of existing sensors. Here, we present the results from flow simulations and laboratory tests of the 3-D groundwater flow sensor. We have used Ansys, a CFD software to simulate sensor performance under a range of flow velocities to assist with design, configuration, and validation of the device. We also present results from tests of the device using a laboratory scale groundwater simulation device that recirculates water at a known velocity through media that is designed to resemble the set-up of an aquifer. We present comparisons between testing of the device and 3-D groundwater flow simulations.