Greetings from Indiana - the hard water state
Water hardness and pH are usually synomonous, but there is a certain
amount of chemistry behind it, which tends to complicate things. Water
hardness is due to the amount of Calcium ions present in solution. The pH
value is due to the concentration of Hydrogen ions in the solution. The
two are related by Carbon dioxide. Most Calcium dissolved in water is in
the form of the carbonate; however the carbonate ion tends to raise the
pH.
Let me (Yawn!) get to the point: A Reverse Osmossis (RO) unit will
remove well over 90% of the Calcium present in hard water. Water
softeners work by replacing Calcium with some other ion, in the
commercial kinds it is usually Sodium, which is actually worse for plants
than Calcium when it builds up. Of course, using RO water which is then
"softened" will introduce very little Sodium, since the RO water
contained very little Calcium to begin with - but is it really worth it?
In my opinion, alkaline water emerging from a RO unit would not concern
me in terms of my plants, rather I might be tempted to think the unit had
simply gotten old and needed a new filter.
Stupid Water Softener Tricks: Might as well pass along a suggestion I
heard awhile ago - use Potassium chloride rather than Sodium chloride to
"recharge" water softeners. The Calcium then gets replaced with
Potassium which is far better than Sodium. In fact, this ought to
really lower the pH if used with RO water. KCl (Potassium Chloride) is
available in health food stores as a salt substitute. Look for little
water softener "pillows" at aquarium shops. Just drop one in the RO
collection reservoir and leave it there until a rise in pH indicates it
needs a soak in the KCL solution (rince well afterwards).
Happy Gardening,
Roger L. Sieloff
PS: Sodium chloride is ordinary salt, a far more benign compound than the
horrible dihydrogen oxide it is sometimes associated with, the latter
substance causing thousands of deaths annualy and millions of dollars of
property damage (not to mention what it does to the atmosphere!!). Fear
not, gentle reader, commercial sources of salt are all but devoid of the
pernicious compound, although it is frequently found in ocean water....