Pure water isn't a conductor. Electrolosis requires a conductor, current, and electrodes. Now, perfectly pure water is hard to get, but still, most needs some help, and then the proper electrodes to produce the hydrogen and oxygen. Not something you generally have to worry about. Assuming (and that can be dangerous) the sensor is designed with any sense, all of the current will be within it, and it wouldn't matter if it ran on 1 volt or 1000 - none of it should leak and potentially result in electrolosis.