Water heater, anode rod, electrolysis, and teflon tape

What you’re describing is an Electrolytic cell (see link in previous post). However, current still needs to flow between the two metals in addition to ion flow through the solution; if that current is not provided directly or via an external current source (battery) the desired electrochemical reaction at the anode rod (and prevention of the oxidation at the heater metal) doesn’t occur.