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Arsenic (As) is a naturally occurring contaminant found in many ground waters. Arsenic in water
has no color, taste or odor. It must be measured by an arsenic test kit or lab test.
Public water utilities must have their water tested for arsenic. You can obtain the results from your
water utility contained with in your consumer confidence report. If you have your own well, you
will need to have the water evaluated. The local health department or the state environmental
health agency can provide a list of test kits or certified labs.
There are two forms of arsenic: pentavalent arsenic (also called As (V), As (+5)) and trivalent
arsenic (also called As (III), As (+3)). In well water, arsenic may be pentavalent, trivalent, or a
combination of both. Although both forms of arsenic are potentially hazardous to your health,
trivalent arsenic is considered more harmful than pentavalent arsenic.
RO systems are very effective at removing pentavalent arsenic. A free chlorine residual will
rapidly convert trivalent arsenic to pentavalent arsenic. Other water treatment chemicals such
as ozone and potassium permanganate will also change trivalent arsenic to pentavalent arsenic.
A combined chlorine residual (also called chloramine) where it does convert trivalent arsenic to
pentavalent arsenic, may not convert all the trivalent arsenic in to pentavalent arsenic. If you get
your water from a public water utility, contact the utility to find out if free chlorine or combined
chlorine is used in the water system.
This Watts Water Quality reverse osmosis system is designed to remove up to 98% of pentavalent
arsenic. It will not convert trivalent arsenic to pentavalent arsenic. Under laboratory standard
testing conditions, this system reduced 0.30 mg/L (ppm) pentavalent arsenic to under 0.010
mg/L (ppm) (the USEPA standard for drinking water). Actual performance of the system may
vary depending on specific water quality conditions at the consumer’s installation. In addition
to the independent laboratory standard testing conditions Watts Water Quality has conducted
additional field testing on our reverse osmosis units to determine trivalent arsenic reduction
capabilities. Based upon Watts Water Quality field testing, it has been determined that the RO
units are capable of reducing up to 67% of trivalent arsenic from the drinking water.
The RO membrane component of this Watts Water Quality reverse osmosis system must be
maintained according to its recommended maintenance cycle. Specific component identification
and ordering information can be found in the installation/operation manual maintenance section,
by phone at 1-800-659-8400 or online www.watts.com
California Proposition 65 Warning
WARNING: this product contains chemicals known to the State of California to cause cancer
and birth defects or other reproductive harm. (Installer: California law requires that this warning
be given to the consumer). For more information: www.wattsind.com/prop65.
Arsenic Fact Sheet
