The general concept probably comes from deaths related to electricity and water.  
My condensed understanding may miss a few points...  The water near the skin is contaminated with salts from sweat, making a fairly decent connection.  The volume of the water makes for a relatively low resistance, like resistors in parallel.  The voltage drop is low due to small current flow, and the couple hundred milliamps needed to cause death can flow.

If you attempt to pass electricity through water at low wattage, water has near infinite resistance.  At higher wattages of DC, electrolysis occurs -- liberating ionic consitituents that have high potential energy and low activation energy (i.e. explosive).  At higher wattages of AC, corrosion of the holding chamber occurs, which increases as the water increases in both pH and temperature.  Depending on the contaminant, you can get a variety of dangerous, smelly, rusty, corrosive, and just plain nasty stuff
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One conductor I think is too often overlooked though is the Earth itself.  This varies by location and moisture content of the soil, but if you sink a couple of even 1 foot test ground rods 100 feet apart, then connect them with wire and an ohmmeter I bet you'll be surprised at how low the resistance is.  Not low enough to be practical at 12 volts, but at 117 or more you could run just 1 hot wire that's insulated and use the earth for the other conductor.  Just ask any cow that's ever dealt with an electric fence.  Most good electric fences can also burn off weeds that come in contact with them, so they're pumping some power through the earth as a return path.  At least maybe you could harvest some earthworms that you drove out of the ground.