I saw this project in the DFRobot newsletter, and thought it might be of interest to some people in this community. I don’t have any knowledge or experience with water quality testing, so I don’t know how practical machine learning truly is for something like water pollution monitoring.
There is a Fritzing diagram, source code, and STL files, but unfortunately the CAD was done in Fusion 360. Still, it seems like the documentation and collection of source files is fairly complete (at least to my untrained eye).