On Thu, Sep 8, 2011 at 12:55 PM, Brendan Gillatt wrote: > On 8 September 2011 10:36, cdb wrote: >> =A0I've been looking at the specifications for a domestic water heater a= nd in >> the sales bumph they specify the minimum water resistivity required (2K7= 95 >> x inches or 1K1 x cm's). I've never seen such a specification before for >> this kind of water heater nor the unit resistivity per area/length. > > I'm assuming this is to ensure shorts don't occur across the heating > coil. Most manufacturers will probably just assume this is safe. > >> I can find no documents on the interrent apart from those referring to >> measurement devices for analytical purposes. > > Electrical resistivity (or conductivity^-1) varies as a function of > salt concentration and temperature--two things that are not absolute > in domestic water supplies. NB: I refer to "salt" here as any ionic > salt, not just table salt (NaCl). It depends on the water quality as whole. Domestic water contains dozens of materials like ; arsenic, mercury, copper, lead and aluminum to name just a few interesting ones.Anything solvable in H2O will result in a boiling point elevation. --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .