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Kathleen Parrott, Blake Ross, Janice Woodard
Virginia Cooperative Extension
Kathleen
Parrott, Extension Specialist, Housing
Blake Ross, Extension Specialist, Agricultural Engineering
Janice Woodard, retired Extension Specialist,Home Management
and Equipment
Foul
taste, smell, or color of your household water may prompt
you to investigate water treatment equipment. The publicity
about water pollution problems may make you question the safety
of your water supply. Or mineral scale buildup may cause you
to invest in early replacement of plumbing fixtures and water-using
appliances.
Before
you attempt a quick and possibly costly remedy, take a first
important step. Have your water analyzed. A water analysis
will help identify bacteria, minerals, or other pollutants
that are present. Interpretation of the test results will
help you determine whether the water needs to be treated and,
if so, the type of treatment needed. The intended use of the
water (whether for drinking, laundry, or all household uses)
will also help determine the extent of treatment required.
Keep
in mind that no single water treatment device treats all problems,
and that all devices have limitations. See
table for common water quality
problems and suggested corrective procedures.
Do not
assume that installation of water treatment equipment similar
to that of your neighbors will be the answer to improving
your household water quality. Different water supply sources,
amounts and types of household uses, and many other variables
affect the selection of the proper water treatment system.
See Quick Reference to Common Water
Treatment Devices
Return
to Table of Contents
Activated carbon filters (also called carbon filters) treat
general taste and odor problems, including chlorine residue.
When water flows through carbon filters, contaminants adsorb
or stick to the surfaces of the carbon particles. Activated
carbon filters are reported to be the best method available
for removing specific organic chemicals, including some pesticide
residues. Studies have also shown that GAC (granular activated
carbon) adsorption is an effective method for radon removal.
Mechanical filters trap, through a straining process, sand,
dirt, and other suspended particles to reduce turbidity in water.
General
Description Carbon filter
devices are available in several sizes and designs. Small units
fit on kitchen taps and treat only 100 to 300 gallons effectively
before a filter change is necessary. Large under-sink units,
often called in-line filters, are designed to treat up to 1500
gallons. On such a unit the canister is connected to the cold
water line. Other styles are available that treat all household
water. An extra filter cartridge or canister is often included
with the initial purchase. Check on availability of filters
and cost of replacement filters at time of purchase; they may
be available from the same dealer, at plumbing supply stores,
or by mail order.
Design
greatly influences efficiency. Variations include use of powdered
carbon or blocks of carbon instead of granular carbon. Those
filters containing more carbon will usually treat more water
before replacement is necessary.
Mechanical
filters are frequently combined with activated carbon filters.
Small mechanical filters, using spun cellulose, attach to
a tap or can be installed under a sink. Filters to treat all
the water supplied to the house may use sand or gravel.
Limitations Activated
carbon filters do not remove nitrate, bacteria, or metals. Concern
about the growth of harmful bacteria in these filters has been
raised in the past. However, recent research by the U.S. Environmental
Protection Agency indicates that the types of bacteria found
in water samples obtained from this type of filter create no
health hazard if the filter is properly maintained. As a precaution,
however, activated carbon filters are recommended for use only
on microbiologically safe water.
Maintenance Setting
up a regular maintenance schedule for filter replacement is
necessary, because there is no easy method for detecting that
a filter is no longer working effectively. The frequency of
filter cleaning or replacement depends largely on the level
of pollutants in the water supply and the quantity of water
flowing through the filter.
A mechanical
filter may become clogged if not cleaned or replaced periodically,
resulting in loss of water pressure and a reduction in flow.
Filters using sand or gravel require automatic or manual backwashing
to remove trapped particles.
Return
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Water
softeners remove the hardness minerals calcium and magnesium.
Water exceeding about 7 to 8 grains per gallon hardness may
interfere with the cleaning action of soaps and detergents,
and cause scale buildup in hot water pipes, water heaters, and
plumbing fixtures.
General
Description The most
common way to soften household water is to use a cation exchange
water softener. A synthetic resin with a strong attraction for
calcium, magnesium, and other positively charged metal ions
(cations) is first saturated with sodium cations from a salt
(sodium chloride) solution. As the water passes through the
resin, the sodium exchanges with calcium and magnesium.
Softeners
are automatic, semi-automatic,
or manual depending on the system for regeneration of the
resin. Each type is available in several sizes and is rated
on the amount of hardness it can remove before regeneration
is necessary.
Limitations Individuals
on a sodium-restricted diet should consult a physician before
using softened water. A possible solution is to have drinking
and cooking water lines bypass the water softener. Water softening
units also remove small amounts of iron. However, using a softener
to remove iron in naturally soft water is not advised. Refer
to the iron filter section of this publication.
Maintenance When the
resin is filled to capacity with calcium and magnesium, it must
be recharged. Fully automatic softeners regenerate on a preset
schedule and return to service automatically. Regeneration is
usually started by a time clock, although some units start regeneration
by water-use meters or hardness detectors.
Semi-automatic
softeners have automatic controls for everything except for
the start of regeneration. Manual units require manual operation
of one or more valves to control backwashing, brining, and
rinsing.
In many
areas, there are companies that provide a water softening
service. For a monthly fee,the company installs a softener
unit and replaces it periodically with a freshly charged unit.
The replacement schedule depends on the water hardness and
the amount of water used.
Return
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Iron filters remove iron and manganese that can cause staining
of clothes and plumbing fixtures. Ferric iron usually appears
as rust colored particles floating or settling in the water.
Ferrous iron is in the dissolved form and cannot be seen in
water. When water containing ferrous iron is exposed to air,
the iron oxidizes and ferric iron is formed.
Water
with a high iron or manganese content is not considered a
health problem, but can be very objectionable in taste, odor,
or appearance if iron is present in amounts greater than 0.3
milligrams per liter or manganese is present in amounts greater
than 0.05 milligrams per liter.
Iron
bacteria are nuisance organisms often associated with soluble
iron in water. Because they cause a slime buildup, they can
be quite objectionable with iron concentrations as low as
0.1 milligrams per liter ferrous (soluble) iron.
The
presence of iron bacteria is indicated by a gelatinous slime
on the inside wall of the toilet flush tank and gelatinous
"rusty slugs" being discharged at the tap. High dosages (200
to 500 milligrams per liter) of chlorine (known as shock chlorination
or disinfection) are required to control iron bacteria. Shock
chlorination must include the well and pumping system.
General
Description and Maintenance Five types
of iron-removal equipment are available:
- Iron
Filter. Iron filters are only useful for removal of
ferrous (soluble) iron and manganese; ferric iron will plug
them. They look like water softeners but contain a bed of
natural or synthetic manganese green sand. Manganese dioxide
oxidizes iron and manganese and the oxidized particles are
then filtered out in the lower part of the bed.
The filter bed must be backwashed frequently to remove
the accumulation of iron particles. For backwashing, a
flow rate more than double the normal service flow rate
is usually required. The exhausted manganese must be recharged
by adding potassium permanganate.
Acid water below a pH of 6.8 will pick up manganese from
the green sand and cause loss of oxygen exchange capacity.
Therefore, neutralization treatment may be necessary.
Also, the slime produced by iron bacteria will clog the
filter.
- Water
softener. Water softeners contain a zeolite mineral
in the resin that will remove soluble iron on an ionexchange
basis (the same way calcium and magnesium are removed in
water softening). Depending on the kind of zeolite used
and the regeneration process, up to 5 milligrams per liter
of soluble iron can be removed. The slime produced by iron
bacteria will clog the zeolite and reduce its effectiveness.
- Polyphosphate
feeder. These units can handle up to 3 milligrams per
liter of iron in solution. They contain a phosphate compound
which coats the soluble iron and prevents its oxidation
when the water is exposed to air. The compound is not effective
against ferric iron that has already oxidized.
Polyphosphate is only effective in cold water. Heating
the water will release the iron so that oxidized iron
accumulates in the waterheater. The heated water will
be rusty and unsatisfactory for home use.
- Chlorinator
and filter. Chlorination followed by filtration through
a sand filter can remove any quantity of iron in any form.
The chlorine oxidizes and precipitates the iron and the
filter strains out the particles. Carbon filtration may
be required to remove excess chlorine residue.
This method also destroys iron bacteria. When the bacteria
cannot be permanently eliminated by shock chlorination,
continuous chlorination is required.
- Aerator
and filter. An alternative to chlorination for iron
removal is that of aeration followed by filtration. An aerator
introduces oxygen into the water, thereby causing ferrous
iron to precipitate through oxidation. Aeration equipment
for household use has become more available in recent years.
Limitations Iron removal
from your water supply can involve complex choices. Careful
planning is needed when iron removal equipment is used in conjunction
with other water treatment equipment. The type of iron removal
equipment chosen depends on the type and quantity of iron in
the water, the characteristics of the water supply, other water
treatment equipment in use, and the user's requirements for
cost, ease of use, and maintenance.
Return
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This system treats corrosive (acidic) water by increasing alkalinity,
resulting in a pH near 7.0. Reducing corrosivity may also lower
the concentration of harmful metals, such as copper and lead,
that may be dissolved from pipe walls and fittings.
General
Description Passing
the water through granular calcite (marble, calcium carbonate,
or lime) is the most common method of home treatment. A mix
of calcite and magnesium oxide also is used. If the water is
very acidic or if a high flow rate is needed, a system to chemically
feed soda ash, sodium carbonate, or caustic soda (sodium hydroxide)
may be necessary.
Limitations
and Maintenance Neutralizers
using soda or sodium compounds increase the sodium content of
water which may be a health concern. Using calcite to neutralize
water increases calcium, which increases water hardness. These
factors must be considered in your treatment choice. All systems
require routine maintenance to replenish the chemical used to
neutralize the water.
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Distillation removes most impurities from water, including minerals
such as nitrate, sodium, and sulfate, and many organic chemicals.
General
Description
Distillation
units boil water to create steam which is then condensed
and collected as purified water. Most impurities remain in the
heating chamber and must be periodically removed. Units vary
from the kitchen countertop size to larger units.
Limitations Removal
of minerals produces water that can have a bland taste. Because
a kitchen location close to point of use is preferred for smaller
units, counter or cabinet space must often be given up. Also,
distillers are expensive to operate.
Some
distillers allow contaminants with a boiling point lower than
water (e.g. some pesticides and volatile solvents) to vaporize
with the water and recondense with the treated water, which
means they remain in the treated water. Others have a volatile
gas vent that releases these products to the atmosphere.
Maintenance Design of
the unit is important because minerals and other contaminants
accumulate in the boiling chamber and can interfere with the
operation of the unit. Hard water can cause scaling in a distiller.
Some units are easily cleaned by hand while others require washing
with a strong acid.
Return
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A reverse osmosis unit substantially reduces
most suspended and dissolved matter from water.
General
Description Contaminants
are removed by forcing water through a membrane having microscopic
holes that allow water molecules, but not larger compounds,
to pass through. Water flushes away the contaminants held by
the membrane.
Membranes
are made of a variety of materials that differ in effectiveness
for different chemicals. Be sure to study water test data
and identify the chemicals to be removed.
Limitations
and Maintenance Although
reverse osmosis removes many organic chemicals, it does not
remove all. For instance, it will not remove chloroform. And
it does not remove 100 percent of most chemicals.
These
units waste large amounts of water. Most units will discharge
up to 50% or more of total water as waste.
The
membrane can develop problems from precipitate buildup and
scaling. A softener must be installed ahead of the reverse
osmosis unit if hard water is used. Otherwise, the minerals
will quickly plug the membrane filter.
Frequently,
mechanical and/or activated carbon filters are installed before
the reverse osmosis unit to remove turbidity and improve taste
and odor. This can result in improved overall water quality
and extend the life of the reverse osmosis membrane.
The
reverse osmosis membrane will need periodic replacement according
to the manufacturer's recommended schedule. Occasional cleaning
and flushing of the whole reverse osmosis unit may be required.
Return
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Chlorination
Both municipal
systems and households can disinfect water by adding chlorine.
Household systems commonly use liquid chlorine bleach injected
into the water by one of several types of pumps.
Chlorination
does not remove nitrate or other chemicals, but may oxidize
organics and some minerals such as iron Chlorine metering
pumps must be calibrated and maintained carefully Using a
carbon filter after chlorination will remove any excess chlorine
and chlorine based chemicals that may form
Other
Methods Other methods
of disinfecting water include boiling distilling pasteurizing
treating with ultra-violet light, and treating with ozone Chlorination
distillation or boiling for 15 minutes are the usual methods
used to purify water for household use. Disinfection by ozonation
or ultraviolet light methods are replacing chlorination in some
water treatment plants, and are becoming more popular for home
uses
Some
filtration units with silver-coated activated charcoal blocks
are being sold for removal or killing of bacteria Before purchasing
such a unit, evaluate it carefully and check for sufficient
test data and certification to assure its effectiveness.
Return
to Table of Contents
When single water quality problems are identified, one water
treatment device may be adequate. In many cases, however, more
than one problem is present, requiring a combination of water
treatment devices. A household treatment system should take
into account the most practical and effective device to treat
each problem, the order these devices should be placed in the
system, and the intended use of the water-- for drinking, laundry,
or all household uses. See diagrams for
typical illustrations of household water treatment devices in
combination.
ACIDITY
- A condition of water when the pH is below 7. See pH.
ALKALINITY
- A condition of water when the pH is above 7. See pH.
BACKWASHING
- The process of reversing the flow of water to restore
or clean a filter.
FLOW
RATE - The quantity of water available or needed commonly
measured in gallons per minute, per hour, or per day.
GRAINS
PER GALLON - The weight of a substance, in grains, in
a gallon. Commonly, grains of minerals per gallon of water
is a measure of water hardness. 1 grain per gallon = 17.1
milligrams per liter.
HARDNESS
MINERALS - Minerals dissolved in water that increase the
scaling properties and decrease cleansing action usually calcium
and magnesium.
ION
EXCHANGE - Process whereby one mineral is substituted
for another.
NEUTRALITY
- A condition of water when the pH is at 7. (neither acid
or alkaline) See pH.
OXIDATION
- Causes the impurities to precipitate, and this reduces
water impurities, such as iron, manganese, hydrogen sulfide,
and many organics.
PEAK
USE RATE - The flow rate necessary to meet the expected
maximum water demand in the system.
pH
- A measure of the acidity or alkalinity of water. Below
7 is acid, above 7 is alkaline.
REGENERATION
- Process which restores the ion-exchange material (zeolite
or resin beads) to useable condition.
SHOCK
CHLORINATION - Using high dosages of chlorine (200 to
500 milligrams per liter)
SOFTENING
- The process of removing hardness caused by calcium and
magnesium minerals.
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Disclaimer
and Reproduction Information: Information in NASD does not represent
NIOSH policy. Information included in NASD appears by permission
of the author and/or copyright holder. More
NASD Review: 04/2002
Adapted
from a publication by Annette Bach and Darnell Lundstrom, North
Dakota State University Extension Service by: Kathleen Parrott,
Blake Ross, and Janice Woodard.
Publication
Number
356-481
,
October 1996
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