I’ve used titanium rod – 1/16″ Dia 6″ length= $1.62 – https://www.mcmaster.com/89145k28
and its easy to crimp a wire to the rod. I might be able to find a picture of it at some point.
Its also possible to drill two holes through a PVC end cap, and then snuggly push the rod through with a watersealant adhesive on it – uses the friction fit of the rod, with the watersealant adhesive as secondary water tight guarantee. That then provides small chamber to protect electrical connections. I used a crimp connections, with solder as a glue, are better for long term survivability.
I haven’t had a lot of field experience with the titanium example though.
One area to look for in ideas of detection is the analog front end of “water leak detectors/alarms” and plant water probes and rain detectors
Part of the issue is that pure water doesn’t conduct. Its the salts/ions that conduct electrons.
So what type of ionic conduction is likely in your water – and more to the point if you have too much current – possibly like in your proposed simple detector – will all the ionic transport be used up. If its flowing water probably not. Rain detectors use a large surface area to catch water and then have a high impedance detection circuit.
These have some good descriptions:
I’m also looking at a water disconnect sensor for stream reaches here in the Western USA. With the long hot summers, the biology of stream pools starts to change when the stream flow reaches zero. Detecting no flow or low flow in a real stream reach is challenging. Perhaps measuring a stream disconnect might be easier and help with stream management. So I’m interested in what your experience is.