wel the resistance play an important role if impedances are not matched there are reflections and so power absorbed by the load can be almost 0 witch actually is what we should want but we need to get the charge to the water molecules for them to break apart The water molecules get charged when the high electric field is applied and retain its charge for a time called relaxation time... it seems a fight between order and heat...
My question to you is what is and where is the load?