I believe that the AquaPlumb system is Capacitive-based! You should be able to make your own, though at that size you may need a capacitance-to-digital converter like the TI FDC1004. I intend to get a free sample from them, and make a very similar system to the Aquaplumb using two pieces of copper tape. Again, these are things that I’ve concept-tested, but need field validation. So much to do, so little time!