I think that water only conducts electricity at above 20v or thereabouts, which is why a car battery wont short underwater, but for example if your mains power gets in the pool it will conduct. I was a bit iffy aswell about electricity and water, but it is just as safe as touching both the terminals on the battery with your fingers, it doesnt conduct. where as if you touch +ve and -ve wires from the mains you get a shock (DO NOT MESS WITH MAINS POWER, IT IS VERY DANGEROUS!)