I'd take a look at eddy currents rather than DC. Think AC motor, not DC: that means there's no electrodes immersed in the water, so no sites at which the obvio

I'd take a look at eddy currents rather than DC. Think AC motor, not DC: that means there's no electrodes immersed in the water, so no sites at which the obvious reactions will occur. There might, of course, be non-obvious ones.