well,...??,,!??
it must be the LIVE extension cord hanging in the bucket of water doing the zapping. But then again, true RO-DeIonized water should have ZERO conductivity, just like distilled water. I would knock the guy what sold you the RODI upside the head, or maybe clean the salt out of the bucket before starting your electrical conductivity experiments.
Electrical maintenance people for the utilities use RODI or distilled water to hose salt deposits off LIVE 500,000 volt coastal high tension power line insulators, from helcopters. the idea being pure water is a great insulator and wont conduct a charge.
You should Check your RODI or clean your BUCKET!!! But by all means, take the power cord out of the bucket.