An inductive loop, (well insulated so shorts are not a problem), lies submerged in a pool of water. Apart from problems caused by possible insulation degradation over time, would the pool of water affect any signals sent along the loop - i.e. 'slugging'/attenuation of the signal?
It depends upon the relative magnetic permeability of water as compared to air. Since the relative magnetic permeability of air is 1.000,000,37 and water is 0.999992 (a vacuum is 1), the effect of water on the inductive loop will be unmeasureable in most practical applications.
According to the OP, the inductor is insulated so that wouldn't be a problem. Question is, why would you want to do that? Heat dissipation? Just put it in a non-conductive bath of oil like a large transformer.
Mineralized water will affect coil inductance --- it's a crucial issue when it comes to using metal detectors, above ground or under water. Mineralized water affecting the signal depends on signal frequency and emission type.
It's not a case of wanting to do it, the loop is part of a rail communications system and the part of the track where it is located floods every now and then.
Aerials on the train pick up signals from the loop inductively.