OurwaterQuality
Staining may be silica, or hardness
Household scaling, or “lime scale”
accumulation, is primarily due to calcium
and magnesium hardness minerals
which can cause damage to plumbing
infrastructure (minor to major disruption
of flow) and fixtures. Many consumers
who use ion-exchange systems (softeners)
in the Santa Fe area also experience
staining - even if their water has all or most
of the hardness minerals removed - that
is confirmed to be silica. We have been
particularly cognizant of high silica levels
because of potential household damage
and the detrimental effects of silica on
salt-free, water-conserving, anti-scalant
systems.
What is silica and why have you perhaps
not heard about it? What I am referring
to is dissolved silica (silicon dioxide),
which is colorless and tasteless. Silica is
unregulated by the EPA, so you won’t
see silica levels listed in your annual
water report. Silica is widely found as an
ingredient in multiple vitamins and taken
as a nutrient supplement. Some consumers
pay big money for the 85 milligrams per
liter (parts per million) silica content, and
the potential health benefits, touted by the
bottler of Fiji water (but that’s yet another
topic). If you had silica levels this high in
your household water, it is likely that you
would be experiencing major silica scaling.
The origin of the high silica content in
Fiji water is attributed to the subsurface
flow of water through silica-rich volcanic
strata. A similar mechanism is believed
to create comparable, and even higher,
silica levels in the Los Alamos public water
supply. Elevated silica levels may be present
in both private wells and in municipal
systems that use well (aquifer) water
sources. Silica levels may be negligible
in supplies from surface waters (such as
rainwater and snowmelt from the Sangre
de Cristo Water Division reservoirs). The
areas of Santa Fe experiencing the highest
silica levels are, in general, the northwest
quadrant and, in particular, Las Campanas,
where we have confirmed lab tests of silica
levels between 65-80ppm.
A simple, although not always definitive,
test for determining whether the scale you
have is hardness or silica is to try wiping it
off with a mild acid such as white vinegar.
If the scale wipes away, it is probably due
to hardness minerals in the water. If the
scale persists, it is likely to be silica. Levels
of 20-25ppm of dissolved silica can cause
staining and can certainly interfere with
anti-scalants.
Can silica be removed from water?
Silica can be removed by anion (negative
ion) exchange, which must be preceded
by cation (positive ion) exchange,
by reverse osmosis, and possibly by
other less-consumptive membrane
technologies. Silica-removal technologies
using hazardous chemicals are widely
used in industrial and municipal
supply applications (in which silica can
interfere with the removal of regulated
contaminants). Neither carbon filters nor
sediment filters remove dissolved silica.
We have launched field research to
verify silica removal technologies at the
residential level through testing green
methods and by using conventional
chemical agents (but only those which can
STEPHEN WIMAN
be re-used rather than discarded). We have
tested electropositive filters and membrane
filtration. Our goal is to offer the greenest
technology that can be documented as
successful in field trials. I will report the
results to our waiting list of interested
customers, as well as in this column.
Stephen Wiman has a background in earth
science (Ph.D. in geology) and is the owner of
Good Water Company in Santa Fe. He may
be reached at 505-471-9036 and skwiman@
goodwatercompany.com.
Reported, printed
and delivered by
your neighbors.
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