Just read the article but am still sceptical as there is mention of tap water containing inhibitors but no mention of rust ,sludge buildup of oxides which i'm sure would dramatically reduce the path of resistance(even inhibitors lose their abilities to stop these problems with age) I would have felt more credibility in the survey had they mentioned old radiator systems aswell as what may well have been laboratory tests on a new system. as mentioned in a previous post by myself although not completely related it showed the conductivity of Dry Floor paint and how a voltage of 115 volts was measured at a distance of 6 feet from a mains source. so sludge filled rads i'm sure would conduct enough to present a hazard, Is there a link to a detailed survey that's been carried out by the IEE on this subject?