In this paper, we introduce a paper-based microfluidic device design that allows liquids to flow at a constant rate through the channels. The device pattern is designed based on a flow rate control test. Our proposed device can be easily manufactured by a wax printer and be printed on filter paper. The primary function of the paper device is to measure the concentration of hazardous chemicals such as heavy metals and bacteria in liquids. We also propose two new image analysis metrics, hue difference and chroma magnitude difference, for analyzing the color of images as a means of identifying the concentration of heavy metals in solutions. In addition, we discuss in detail the image processing pipeline for analyzing the devices from the initial image capturing to segmentation and analysis. This paper also discusses future goals and possible directions to take, such as handling the device from different viewpoints.