hard tap water

"Racf" wrote in message .net...
I believe you may be mistaken on this point about a raise in TDS, or for
that matter the two for one exchange of Sodium with either Calcium or
Magnesium. I see little to no conductivity change in softened water and
have read many times that TDS is unaffected using these units. Whats
your source for this information?

Cation exchange is commonly discussed in college-level chemistry
texts. You'll see that the two-for-one exchange is necessary if you
think about the charge balance. You can't replace Ca++ or Mg++ with
Na+, because then the water would become negatively charged. Two Na+
ions are released, and you're left with CaCl2 or MgCl2 in the water
softener.

As to TDS, if you measure in mg/L (or equivalently ppm), the effect
will be different depending on your ratio of Ca to Mg. Na weighs
almost as much as Mg, so replacing Mg with 2 Na will increase TDS. On
the other hand, Ca weighs almost twice as much as Na, so replacing Ca
with 2 Na will have almost no effect on TDS. So if your hardness is
mostly Ca, you're correct, TDS will change only very slightly.

When I said TDS, what I really meant was the total number of dissolved
ions. This will go up as a result of the cation exchange, even if the
weight of the dissolved solids changes only slightly.

- Jim