Iron and Manganese in Household
Water
Prepared by:
Glenda M. Herman, Extension Housing Specialist
Published by: North Carolina Cooperative Extension Service
Publication Number: HE-394
Last Electronic Revision: March 1996 (JWM)
Iron and manganese are minerals found in drinking water
supplies. These minerals will not harm you, but they may cause
reddish-brown or black stains on clothes or household fixtures. Under
guidelines for public water supplies set by the Environmental Protection
Agency (EPA), iron and mangenese are considered secondary contaminants.
Secondary standards apply to substances in water that cause offensive
taste, odor, color, corrosion, foaming, or staining but have no direct
affect on health. The standard Secondary Maximum Contaminant Level (SMCL)
for iron is 0.3 milligrams per liter (mg/L or ppm) and 0.05 mg/L for
manganese. Private water supplies are not subject to federal standards,
but these standards can be used as guidelines to evaluate the quality of
water from wells or springs.
The four forms of iron and manganese commonly found in
drinking water are ferrous, ferric, organic and iron bacteria. Normally,
water appears clear when first drawn from the cold water faucet. If yours
is not, it may contain ferric iron or organic iron. Both color the water.
Ferric iron precipitates or settles out. Organic iron does not settle out.
In well water, insoluble iron oxide is converted to a soluble form of
ferrous (dissolved) iron. Ferrous iron is colorless, but when in contact
with air, it oxidizes readily, creating reddish- brown, solid particles
that then settle out as ferric oxide. Manganese is similar to iron but
forms a brownish-black precipitate and stains. Manganese is less commonly
found in groundwater than iron, rarely found alone in a water source, and
generally found with dissolved iron.
Health Considerations
The presence of iron and manganese in water is not
considered health problem. In fact, small concentrations are essential to
human health. However, high concentrations of iron may give the water an
unpleasant metallic taste while still being safe to drink. When iron
combines with tea, coffee, and alcoholic beverages, it produces an
unappetizing inky, black appearance and a harsh, offensive taste.
Vegetables cooked in iron-contaminated water turn dark and look
unappetizing.
Iron bacteria (a harmless bacteria), occur in soil,
groundwater, and some surface waters. Iron bacteria are considered harmless
to health, however, they may give water an off taste or color, cause
splotchy yellow stains on laundry, and clog water systems. Iron bacteria
usually appear as stringy, slimy, mucous-like substances suspended in
fresh water and may be colored brown, red, or white. They thrive on iron
in the sink or metal parts of the water system and are most easily seen on
the inside surface of the toilet tank.
Testing
A water analysis should be done to determine the source
of the iron and manganese. Iron and manganese may be present in the water
supply or be caused by corroding pipes (iron or steel). Iron from pipe
corrosion indicates low pH that may need to be corrected.
A water treatment equipment company or testing
laboratory can test water for dissolved or oxidized iron or manganese.
Call the North Carolina Cooperative Extension Service center in your
county or the public health office for names of laboratories that perform
tests for colloidal or organic-complexed iron and manganese.
Ask the testing laboratory how to collect a water
sample for an iron and manganese test. Generally, you should take the
sample from the faucet closest to the pump. Allow the water to run for
5-10 minutes before sampling to obtain fresh water that has not been
exposed to air. Do not sample water that has gone through a water heater
or a water treatment unit such as a softener. If the water is clear when
first drawn, but red or black particles appear after the water settles,
dissolved iron and manganese are present. If the water has a red tint but
no particles settle out after a time, colloidal iron is the cause. Reddish
brown or black brown slimy masses inside the toilet tank indicate iron or
manganese bacteria. Laboratory tests are recommended in all cases to
determine iron and manganese concentrations.
Treatment
Iron and manganese treatment should be based on a
chemical analysis of the water showing the type and concentration
present. There are five treatment methods for the removal of iron and
manganese from home water systems.
WATER SOFTENER (CATION EXCHANGE)
A water softener can remove small amounts of ferrous
iron and manganese. Iron and manganese in untreated water are flushed from
the softener medium (ion exchange) by backwashing (forcing sodium-rich
water back through the unit). This process adds sodium to the resin
medium, and iron and manganese are carried away in waste water.
The amount of iron and manganese a softener can remove
depends on the water properties, the types of regeneration and backwash
controls, and the ion exchange resin or zeolite used. You must maintain a
clean resin bed by frequent and thorough backwashing and regeneration.
Manufacturer literature should be carefully studied and system set-up and
operation instructions followed. Caution: Water softeners treat hard water
by adding sodium to the water, a health concern for people on
sodium-restricted diets. For this reason, you may want to connect a
softener only to the hot water line leaving cold, unsoftened water for
cooking and drinking. In iron and manganese removal, the softener must
treat both hot and cold water since sinks, laundry, and dishwashing
equipment are affected. A separate tap can be installed to provide
unsoftened water for cooking and drinking.
AERATION
Dissolved iron and manganese are easily oxidized to a
solid form by mixing with air. A pressure aerator mixes air with the
water, the air is vented, and then the solid particles are filtered from
the water.
This method adds no chemicals to the water and is most
effective in warm climates. The filter must be backwashed frequently to
properly maintain the system. To protect the water from contamination by
bacteria in the air, the system should be totally enclosed and only
biologically safe water should be used. The appropriate pumping capacity
must be maintained for adequate air intake.
OXIDIZING (CATALYST) FILTER
When the total combined iron and manganese
concentration is less than 15 mg/l, an oxidizing filter (natural
managanese greensand, manufactured silica gel zeolite coated with
manganese dioxide, plastic resin beads, or pumicite), is recommended. Some
filters are coated with a manganese oxide and are regenerated by using a
potassium permanganate solution. An oxidizing filter supplies oxygen to
convert ferrous iron into a solid form which can be filtered out of the
water.
Frequent backwashing and stirring of a manganese
greensand bed helps prevent an iron-fouled bed. After several weeks of
use, the greensand filter should be backwashed with potassium permanganate
to remove solid particles and regenerate (recoat) the greensand to allow
absorbation of more dissolved minerals. Synthetic filters, such as zeolite,
requires less backwash water and softens the water as it removes the iron
and manganese.
CHLORINATION AND FILTRATION
When the iron and manganese content of the water is
extremely high (above 10 ppm), a combination of chemical treatment and
filtration is necessary. Small chemical pumps are used to add chlorine
bleach, potassium permanganate, or hydrogen peroxide into the water. After
a retention time of at least 20 minutes to allow for oxidation of ferrous
iron into the insoluble ferric form, the solid particles are filtered out.
When chlorine is used, the treated water can have an
unpleasant taste if a particle filter of calcite, sand, anthrocite, or
aluminum silicate is used. Use an activated carbon filter to remove both
excess chlorine and solid iron and manganese particles. Backwash
frequently. Some units have an automatic backwash cycle.
OTHER TREATMENTS
Complexation is a simple and low cost method for
removing iron and manganese up to 3 mg/L. A phosphate compound is added to
the water to complex (tie up) the dissolved iron or manganese. However,
adding phosphates to water supplies is not allowed by law in North
Carolina.
If organic-complexed or colloidal iron/ manganese is
present in the untreated water, a longer contact time and higher levels of
chemical are necessary for the oxidation reaction to take place. Aluminum
sulfate (alum) eases filtration by causing larger iron/manganese particles
to form.
A multistage treatment operation may be necessary if
your water has high levels of iron and manganese and they are in both the
dissolved and solid forms. For example, the water could first be aerated,
than chlorinated to oxidize residual iron and kill iron bacteria, and then
filtered through a mechanical device to remove particles. This can be
followed by activated carbon filtration to remove excess chlorine and a
water-softener for hardness control as well as removal of any residual
dissolved iron and manganese.
Summary of Treatment Options for Iron and Manganese
| Symptom |
Cause |
Treatment |
| Water clear
when drawn, reddish-brown or black particles appear as water stands;
reddish-brown or black stains on fixtures or laundry. |
Dissolved
iron or manganese. |
Water
softener (less than 5 mg/L of iron) Aeration (less than 25 mg/L of
iron). Oxidation/Filtration (less than 15 mg/L of iron plus
manganese). Chlorination-Filtration (greater than 10 mg/L of iron). |
| Water
contains reddish-brown particles when drawn; particles settle out as
water stands. |
Iron
particles from corrosion of pipes and equipment. |
Raise pH with
neutralizing filter that also filters particles. |
| Water
contains reddish-brown or black particles when drawn; particles settle
out as water stands. |
Oxidized
iron, manganese, or both due to exposure of water to air prior to tap. |
Particle
filter (if quantity of oxidized material is high, use larger filter
than in line, e.g. sand filter). |
| Reddish-brown
or black slime appears in toilet tank or from faucet. |
Iron
bacteria. Manganese bacteria. |
Kill bacteria
masses by shock treatment with chlorine or potassium permanganate,
then filter; may require continuous feed of chlorine or potassium
permanganate, then filter. |
| Reddish or
black color that remains after 24 hours. |
Colloidal
iron, manganese, or both. Organic-complexed iron, manganese, or both. |
Chemical
oxidation with chlorine or potassium permanganate. |
Summary
Iron and manganese are common household water
contaminants with no known direct health effects at levels found in water.
Their presence may cause staining and offensive tastes and odors.
Treatment of these secondary contaminants depends on the form in which
they occur, and the levels of concentration. Iron and manganese removal,
bacteria control, water softening and treatment for any other
contamination may be separate problems, yet they must be considered
together. Accurate testing is important prior to selection of a treatment
system. The table on page 3 may help you identify and determine
treatment(s) for iron and manganese in household water supplies.
References
Kolega, John J. Water Conditioning and Treatment of
Iron and Manganese. Fact Sheet 9. University of Connecticut
Cooperative Extension Service. 1989.
Machmeier, Roger E. Iron in Drinking Water.
University of Minrkesota Agricultural Extension Serivce. 1971.
Plowman, Faye T. Iron and Manganese. Fact Sheet
5. University of New Hampshire Cooperative Extension Service. 1989.
Wagnet, Linda and Ann Lemley. Iron and Manganese in
Household Water. Fact Sheet 6. Cornell Cooperative Extension. 1989.
------------------------------
Reference:
"Iron and Manganese in Household
Water," Water
Quality & Waste Water Management. North Carolina
Cooperative Extension Service. July 2, 2004
<http://www2.ncsu.edu/bae/programs/extension/publicat/wqwm/he394.html>. |
