Can I apply RFID chips in wastewater poured into wash tanks, toilets, etc., and set up RFID signal receivers on sewage manholes in order to track those chips?
Passive LF and HF tags can be read in water, but the read range is likely not long enough to work for your application (I assume there could be a distance of 5 feet or more between the waste water and manholes). If you tried this with a passive UHF RFID tag, the water would absorb the RFID energy and detune the energy. I believe you could, however, develop a special passive UHF tag that would sit above the water on something that floats (a piece of light plastic, for example). A reader would then be able to pick up the signal.
You'd have to ensure the tag sat above the water and that it would not capsize. In addition, the tag would need to be small enough to go down a drain or a toilet. Shrinking the size of the tag would reduce its read range, so you'd likely need to perform a bit of engineering to make a tag that is small enough and would float on water. There is no off-the-shelf tag that would fit the bill, to my knowledge, but there are companies that could make such a tag.
—Mark Roberti, Founder and Editor, RFID Journal