Re: RO

Mike (who has a water softener on his very hard water and just installed an
RO/DI unit):

I think the RO is a great idea for you (if you do discus).  I think the DI is
silly.  Let me see if I can explain why this is so.  The main cations (metals)
in your water are Ca (calcium) and Na (sodium).  Others present may be Mg
(magnesium), Fe (iron), etc. depending on just what your water is like.  Your
water softener is a DI unit that exchanges every metal but Na for Na, so coming
out of the Culligan (or whatever) the water is now higher in Na but lower in
everything else.  In fact, thinking of the Ca alone and neglecting the high
sodium, yours could be used directly out of the softener.  You have decided to
reduce the sodium, probably a good idea, as well as further reduce the Ca (may
be good or not, there is such a thing as too little Ca).  An RO will do this. 
And the output of your RO should be down in the 70 ppm or 150 usiemens
(conductivity) range.  Now a bit of that will be Ca, and the DI in your RO/DI
will exchange that for Na.  But WHY would you want to further reduce the Ca? 
Seems just fine as it is.  If I were you, I would get a RO without a DI.  If
you are going to use softened input, I think the DI is not very useful and
possibly harmful.   Incidently, I notice that you have a fair amount of Mg.  It
behaves somewhat similarly to Ca, so the notes above will pretty apply to it
too.   Dave

Dave Gomberg, Experimenta      San Francisco CA USA   gomberg at wcf_com