United States
Environmental Protection
L Agency
This fact sheet helps water system owners and operators understand and respond to issues that may arise with arsenic
in the distribution system, or with distribution system concerns resulting from the installation of arsenic treatment.
Although arsenic is measured at the entry point to the distribution system for compliance determinations, you should be
aware that arsenic levels could increase in the distribution system at any time due to a number of factors. It is important
to remember that any process changes, including chlorination, can impact your distribution system and the water quality
at customers' taps.
Arsenic Can Build Up on and Release in
Pipes and Storage Tanks
Public water systems with arsenic in their raw water may
find that scales on pipes and other components in their
distribution systems contain relatively high arsenic
concentrations. These arsenic-rich scales can become
dislodged and suspended in the water, and may be
ultimately delivered to consumers.
Arsenic has been shown to attach to iron in distribution
system pipes. Because iron is so effective at binding with
arsenic, corrosion deposits can have high concentrations
of arsenic solids. In a recent study, arsenic levels found in
solids that were collected after pipe sections and hydrants
were flushed were as high as 13-65 milligrams of arsenic
per gram of solid. Most of the remaining solid was
composed of iron.
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It is known that even if your water has detectable levels of
arsenic that are below the 0.010 mg/L MCL, and you have
iron pipes or components in your distribution system, your
system's pipes may have arsenic-rich scales attached to them.
As long as the scales are not disturbed, they will remain
attached to the pipes or other distribution system compo-
nents. Certain conditions, such as flushing of mains or
fire flow conditions, may result in those scales being
sloughed off and suspended in the water, releasing the ar-
senic. Other conditions, such as changes in water chemis-
try, may result in some of the arsenic dissolving back into
the water. Both of these situations could cause high ar-
senic levels at consumers' taps.
Arsenic Control Measures Can Affect
Finished Water Quality
Public water systems installing arsenic treatment should
be informed about possible changes to their finished water
that may result from the arsenic treatment they install.For
example, systems may need to adjust their finished water
quality to address new concerns about corrosion. Changes
in water chemistry due to using new sources, blending
different source waters, or installing arsenic treatment are
some of the factors that can affect distribution system water
quality. In some cases, this may cause an increase in arsenic
levels in the distribution system or create simultaneous
compliance issues with other drinking water regulations.
Is Arsenic in your Storage Tank?
Water systems may also find deposits of arsenic-
rich particles in their storage tanks or at locations
in their distribution system with low flows. If the
flow is increased or a storage tank is drawn down
to a low level, these arsenic-rich particles can get
stirred up and transported to consumers' taps.
This situation occurs primarily when iron media
used in treatment are released into the distribution
system, or when iron particles are not properly
filtered out during iron removal treatment. If these
treatment technologies are operated correctly, this
should not be a problem for most water systems.
Is Your Ground Water System Installing Disinfection for Pathogen Control?
Water systems that disinfect their water should be aware of the possibility of an increase in arsenic concentrations
in their distribution system, particularly if the water contains high concentrations of dissolved iron. When
chlorinated, the dissolved iron forms particles on which arsenic can accumulate. As a result, high arsenic
concentrations may occur in distribution system water even if arsenic concentrations in the raw water are
below the MCL.
This happened to a small community water system in the Midwest that began chlorinating water from a series
of wells that had raw water arsenic levels between 0.003 and 0.008 mg/L and iron concentrations up to 0.4 mg/
L. At the same time, the system installed a polyphosphate feed system for corrosion control. Soon after
chlorination began, the system received intermittent colored-water complaints from its customers with increasing
frequency across the distribution system. Samples collected from several representative locations throughout
the service area had a reddish-brown color and contained particles. A metals analysis showed high levels of
copper and iron oxides in the finished water, along with arsenic concentrations approaching 5 mg/L. Because
of the water's colored appearance, it was considered unlikely that customers would consume the water. Doctors
and health care professionals were notified of the situation and instructed to watch for signs of arsenic poisoning.
—Continued on page 3
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—Continued from page 2
Researchers found that chlorinating the water caused the formation of ferri-
hydroxide solids. The minimal arsenic present in the groundwater was being
concentrated as it absorbed onto the solids. Copper oxide particulates also formed
and were released. To some extent, the polyphosphates served a useful role by
keeping iron in solution and counteracting the tendency for the iron oxides to
form, but additional steps were needed. For six months the system alternated
their chlorination schedule: on for one day then off two days. The system then
returned to full-time chlorination, starting with a low distribution system residual of
0.2 mg/L and gradually increasing it to 0.5 mg/L. The system continued to flush
water mains on a semi-annual schedule using a unidirectional approach. In the
last year, the system received only one colored water complaint.
For more details on this case, see "Well Water Disinfection Sparks Surprises"
by Steve Reiber and Glenn Dostal, Opf low Vol. 26 No. 3, March 2000.
Hypochlorination System
*• Switching to a New Source or Blending Sources
If you plan on switching wells or blending sources to meet
the arsenic MCL, remember that the new well's water may
react differently in your distribution system than the water
you were using before. Be sure you understand the new
well's water quality characteristics like pH, alkalinity, and
iron and manganese concentrations. Changes in these water
quality parameters could impact lead and copper as well as
arsenic levels, disinfection byproducts, and aesthetic
characteristics like taste, odor, and color.
> Reducing pH During Treatment
Some arsenic treatment technologies require the pH to be
reduced as a treatment step. If your system has adopted
one of these techniques, be sure your pH is raised to a level
that will not cause corrosion problems in your pipes. If
you already have a corrosion control program in place,
review whether you will need to adjust your corrosion
chemical dose in response to any change in your water
quality resulting from the installation of arsenic treatment.
Keep in mind that adjusting the pH upward for lead and
copper control may also cause arsenic to be released from
scale on pipes and components.
* Installing a Treatment Technology that Uses Iron
If you have installed an arsenic removal treatment
technology that uses iron, you should not see elevated levels
of iron in the water entering the distribution system if the
treatment technology is being operated properly. However,
if the treatment technology has been recently installed and
operational adjustments are still being made, you may see
elevated iron levels after treatment. You may also see elevated
iron levels if you are blending with iron-rich water. In these
cases, keep in mind that arsenic adsorbs onto iron, and the
iron may deposit in your pipes and storage tanks. This
arsenic-rich iron could dislodge and be re-suspended in
the water when flows increase. If this happens, consumers
may receive pulses of water containing high levels of arsenic
and iron, and should be warned not to consume the water
if it appears rusty in color.
» Using Activated Alumina or Enhanced
Coagulation with Alum
If you plan on using activated alumina or enhanced
coagulation with alum to treat your water, consider testing
the water periodically for aluminum in the distribution
system. While not a concern in terms of health effects,
aluminum concentrations as low as 0.05 mg/L can result in
customer complaints about particles or color in their water.
How Can I know if Arsenic is a Problem in
My Distribution System?
Drinking water regulations require public water systems
to monitor for arsenic at the entry point to the distribution
system. There is no federal requirement for systems to
monitor for arsenic within the distribution system. You
may, however, want to test your distribution system water
for arsenic to be sure that the water being delivered has
arsenic levels below the MCL. If you decide to monitor
your distribution system, consider testing for arsenic at
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locations where the settling and accumulation of iron solids
or pipe scales are likely (i.e., areas with cast iron pipe, ductile
iron pipe, or galvanized iron pipe).
If your water system has installed some form of arsenic
treatment, keep in mind that the treatment you installed
may change the water quality in other ways. It might cause
the water to react differently in the distribution system.
Depending on the kind of treatment you've installed,
consider what distribution system problems might result.
A change in the taste, odor or appearance of the water at
customers' taps may be the first indication of a problem.
Some water quality parameters to consider monitoring,
depending on your arsenic treatment technology, include
iron, pH, manganese, alkalinity, and aluminum.
How Can I Prevent Arsenic
Accumulation in My Distribution
System?
There are a number of management techniques that
can be used to help keep arsenic levels low in the
distribution system. They include:
• Optimize treatment operations for turbidity
removal.
• Check finished water pH and alkalinity after
arsenic treatment is installed. If they have
changed, consider whether corrosion control
practices need to be modified.
• Adopt a unidirectional flushing program for water
mains.
• Clean and maintain your storage tank(s).
• Optimize distribution system operations to
minimize water age. This practice will prevent
sediment accumulation and water quality
deterioration.
• Operate valves and hydrants to avoid sudden
changes in flow direction or velocity. This
practice will prevent the resuspension of
sediments into the water column.
• Monitor arsenic levels at drinking water taps,
hydrants, and low flow dead-end areas.
What Should I Do if Distribution System
Arsenic Levels are High?
»• Consider Notifying the Public
Even if your water system has not violated the arsenic
standard, you may want to notify consumers that you have
detected arsenic levels in the distribution system exceeding
the MCL. If you make such notice, consider using the
following standard public health effects language for
arsenic:
Some people who drink water containing
arsenic in excess of the MCL over many years
could experience skin damage or problems
with their circulatory system, and may have
an increased risk of getting cancer.
You may also want to explain how you plan to fix the
problem. For example, if you plan on cleaning or flushing
the distribution system to remove scale from the pipes,
explain briefly what you will be doing, when you'll be doing
it, and when you expect the problem to be addressed.
* Consider Distributing EPA's Consumer Fact
Sheet on Arsenic
EPA has developed the fact sheet Arsenic in Your Drinking
Water—-Just the Facts for Consumers that explains the health
risks associated with having elevated levels of arsenic
in your drinking water. This fact sheet is available on
the web at http://www.epa.gov/safewater/arsenic/
basicinformation.html. Color copies are also available by
calling the Safe Drinking Water Hotline at 1-800-426-
4791. Consider distributing the fact sheet as part of your
public education effort if you think you have arsenic prob-
lems in your distribution system.
For More Information on Managing Your
Distribution System:
Distribution Systems: A Best Practices Guide
(EPA# 816-F-06-038)
AWWA 2004. AWWA Standard G200-04: Distribution
Systems Operation and Management. Denver, CO.
Lytle, D. A; Sorg, T. J.; Frietch, C. 2004. Accumulation
of Arsenic in Drinking Water Distribution Systems.
Environ. Sci. Technol. 35(20); 5365-5372.
Distribution System Research — http://www.epa.gov/
nrmrl/wswrd/ dw/ dsr.html
Office of Water
www.epa.gov/safewater
EPA816-F-07-005
April 2007
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