In some of the justifications I have seen for the ground mat under the fiberglass pool it was mentioned that they may be somewhat conductive. Although this is a very high resistance it still might be enough to get some stray voltage to the water across the thousands of square feet of material. With all the chjemicals in pool water I bet it is more conductive than you would think.
Some years ago I did some conductivity studies on water in a white bucket with 120v, 1 foot copper probes about a foot apart, a 60w light bulb and a meter. I don't remember all the details but I do know it didn't take many impurities (salt in my test) in the water to light the bulb. Maybe I will get a few minutes some day to do it again with pool water.
