T&T: Deionized water -- bacteria and corrosive effects.

[Ken Bloomfield]

Well, not quite the last from me after all. This touches one two subjects:

   1. A bit more on the corrosive effects of water that has been
      stripped of its ions via ion exchange cartridges, and
   2. A bit more for the long term tank problem query, which, however,
      was referenced to a reverse osmosis system.

*DEIONIZED WATER* -- The comment that "the product water from a 
"spot-free" or softener by any other name is NOT deionized" is 
conventionally probably correct, but I do think it needs qualification. 
To the best of my knowledge, the water "spotting" that spot free 
filtration systems attack is the total dissolved solids in the water. 
This is done using ion-exchange resin beds. However, these beds can be 
of different types. The following is a simplified version of these beds, 
and what to watch out for:

        * Ion exchange systems are commonly comprised of many small
          polymer beads with special attributes to attract certain ions.
        * These beads are packed together and held in place in the
          cylinder by a frit, and are commonly called a resin-bed.
        * These beds "go after" (i.e. attack/capture) the ions
          associated with the materials they are set to capture (e.g.
          the cationic substance calcium).
        * These beds may be made to go after anions (- charge) or
          cations (+charge).
        * Simple water softener ion exchange cartridges will usually
          have a bed that goes after the calcium cations and "trades
          them" for sodium ions, and will not produce corrosive water.
        * De-ionizing water is produced when a so-called mixed-bed resin
          bed system is used, with one bed trapping cations and a second
          trapping anions.
        * Therefor, it is important to know if the filter has a mixed
          bed, or is simply a calcium stripping single bed system.  If
          it is a mixed bed system, you will produce substantially
          deionized water.  If not, then you likely will have no
          corrosive problems.  I did a bit more checking on the
          "Stain-Less" filter, and in fact it apprears to be a single
          bed cation resin-bed system, since on their site they say that
          the calcium, etc. is exchanged for sodium in the output water,
          thus implying that it is like a simple household water
          softening system in resin-bed terms, but does also say that it
          removes chlorine.
        * Since, as in the case of the "Stain-Less" filter, some
          "spot-free" filters will strip the chlorine from the water as
          well at the calcium, -- you are left with a big tank of water
          with no bactericide, not to mention your water pump and
          plumbing void volumes -- and IMHO that is asking for trouble.
        * It is not very difficult to filter after the tank/pump and
          near the end of the plumbing, thus leaving the beneficial
          chloramines the maximum chance to do their job, and still
          achieve good tasting water.  I can think of no good reason not
          to do so.  If worried about solids buildup in the tank bottom,
          then a particulate-only filter prior to the tank should suffice.

    *REVERSE OSMOSIS WATER* -- I think that the Wikipedia website that
    deals with "REVERSE OSMOSIS" at:
     *http://tinyurl.com/kzt4x
    *does a good job of commenting on this approach, however, one snip
    from there is worth posting here:
    /"The desalinated water is very corrosive and is "stabilized" to
    protect downstream pipelines and storages usually by adding lime or
    caustic to prevent corrosion of concrete or cement lined surfaces."/
    As such, since I don't have a watermaker, and thus don't know for
    sure if they normally have a post-osmosis stabilization process or
    not, I recommend reading that full site.

    Hope this helps.
    Ken Bloomfield
    Tellico Lady,
    50' Marine Trader
    Maryville, TN