OK, so here's a simple one. When current flows through a wire, it produces a tiny magnetic field. If you bend the wire into a spiral, the fields of each loop merge together forming a field you can actually measure.
But does the conductor have to be metal, or would any conductive material work? E.g., would a plastic tube full of water still produce the same magnetic field? [Assuming the water has enough impurities to be considered a "conductor" to start with, which it usually does.]
Edit for Clarification: OP is talking about a simple electromagnetic coil, without regard to core material or application. Assuming Air Core, would a coil of water in pvc tubing, electrified, produce a measurable magnetic field?