Random SHOCK!

[Delphinus]

Good grief Charlie Brown .. don't be testing for stray current with your finger. No multimeter in the house?? No GFCI?? If I had nothing to work with I would unplug everything and check each item over one by one, usually you can see a little crack or something if it has let go.

As you surmised it's probably not your lights unless there is a conductive path from the lights to the water. It's one of your pumps or your heater, gotta be.