You sweat when in a hot tub. Gradually the salt content rises.
It exists as ions in solution -- and they are effected by magnetic fields.
( Which is why sub-sea transmission is done by DC only. AC just stirs the ocean and kills transmission economics.)
It is critical that all in one hot tubs have a true ground from the three prong plug. A GFCI is built-in -- but a true ground is necessary to bleed off the voltage induced into the pool as it circulates past the magnetic fields of the pump motor - - and, no, the typical design does NOT have a Faraday cage in anyway shape or form blocking the field windings from sweeping through the bath water.
This kind of induced voltage can reach painful, even lethal levels. I've personally tested voltages as high as 47V from bath to ground. Multiply that by your wet sweaty skin and the mass of circulating salts and you have a real hazard.
The help line from the tub manufacturer was helpless/ clueless.
http://en.wikipedia.org/wiki/Hall_effectThe physics of the energy build up is due to the Hall effect. The salty bath water is the conductor and the pump motor provides the electric field and drives the ionic water across the lines of force.
The ions are the charge carriers.
MHD power plants are based on the exact same phenomena -- flipped. They use hot coal fired gases injected with K or Na to rocket through an expansion nozzle wrapped in DC field windings and in passing directly induce DC power.
http://en.wikipedia.org/wiki/MHD_generatorWhen a hot tub is placed on a non-conducting surface and the voltage is not bled off it can build to astounding levels. It ends up becoming a gigantic big wet capacitor. Then one fine day the deck is wet and a path to ground is made. Wham! Trouble.
