Agriculture accounts for 85% of the world's freshwater usage. Drip irrigation significantly reduces water usage and has been adopted by many farms, orchards, and vineyards. Rubber or PVC tubing is fitted with thousands of drip emitters whose water pressure and flow are controlled by a small number of valves resulting in suboptimal use of water resources. While UAVs and other sensors can be used to determine water needs and compute appropriate emitter settings, it is currently not possible to close the loop: adjusting flow at the individual plant level to compensate for variations in plant and soil properties, elevation, sun-angle, evapotranspiration, drainage, and emitter contamination by dirt or insects. We propose retro-fitting existing systems with low-cost, passive, plastic, screw-adjustable emitters that are commercially available. This paper presents a design for an automated device that would allow passive emitters to be systematically adjusted in the field by human and robot teams to fine-tune water delivery at the plant level. This paper describes the mechatronic design, prototype, and initial experiments with a hand-held version of the device with a coarse-to-fine mechanism to facilitate alignment to passive emitters in the field and precise automated adjustment of flow settings. We report experiments with an implemented prototype that can compensate for orientation error up to ±39 degrees and position error up to ±42:5mm when adjusting a 16mm emitter cap.