Archive version -- See extension.missouri.edu

Archive version -- See extension.missouri.edu
AGRICULTURE
Understanding Home Water Treatment Systems
T
for drinking and cooking may be more cost effective than
owning and maintaining equipment.
Water treatment systems generally use one or a
combination of these five basic methods:
• Disinfection methods (chlorination, ultraviolet light,
etc.)
• Filtration, including activated carbon filters
• Reverse osmosis
• Distillation
• Ion exchange (water softeners)
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‌he home water treatment industry has responded
to public concern over water quality by
introducing a variety of home water treatment
products into the marketplace. When faced with so many
choices, consumers wonder what, if any, water treatment
system they need. The various methods for treating
water and some of the advantages and disadvantages of
those methods are described in this guide. This is not
an endorsement of any particular method or product for
treating water in the home.
If you are on a public drinking water supply, your
system most likely meets national safety standards. Home
treatment should not be needed for health protection.
Homeowners using a private water supply, however,
are responsible for monitoring the quality of their own
drinking water supply. Water treatment devices can
improve the quality of water by reducing health hazards
such as bacteria, chemical pollutants and other toxic
substances, or help remove nuisance problems, such as
odors or hardness.
Before considering any treatment devices, you
should know the quality of your water supply. Odor and
hardness problems can sometimes be detected by simple
observation. Detection of bacteria, potentially toxic
substances and other contaminants usually requires
laboratory-conducted tests. If any undesirable qualities are
identified in the water, the problem can often be solved by
repairing or replacing the existing water system or treating
the home water supply.
Locating a safe water supply is usually the best solution
to combat a health risk. When persistently contaminated
water poses a health threat or makes the water unusable,
consider the following options:
• Correct well construction faults
• Eliminate sources of contamination
• Install a new private well
• Connect to a public water supply
• Develop a community water system
After considering all of the options, a home water
treatment system may be the most economical choice. Be
sure the system you select bears the mark of the National
Sanitation Foundation (NSF).
Before purchasing a system, you should know how the
various systems work, what problems they address and the
maintenance required. If more than one problem exists,
treating water can become complicated. Purchasing water
Disinfection
Disinfection methods kill most of the harmful bacteria,
viruses, cysts and worms found in water that can cause
acute illness. Disinfection methods include chlorination,
pasteurization, ultraviolet light and boiling
Chlorination
The most common, oldest and relatively inexpensive
method used to disinfect water is chlorination. A chemical
feed pump continuously dispenses chlorine chemicals into
the water supply. Chlorine, an oxidizing agent, kills most
bacteria and some viruses. In the proper concentrations
and under adequate exposure time, chlorine is an excellent
disinfectant.
However, care must be taken to ensure that only clean,
clear water is used. Chlorine reacts with certain metals
and organic matter in the water. The major problem with
chlorination is the potential formation of hazardous,
chlorinated, organic chemicals (trihalomethanes) when the
chlorine reacts with organic molecules in the water supply.
Using an activated carbon filter after chlorination will
remove excess chlorine and limited amounts of chlorinated
chemicals formed. Chlorination may also oxidize and
remove some color and odor-causing substances including
some iron and hydrogen sulfide.
The chemical feed pump requires frequent maintenance.
The chemical reservoir must be kept filled and the pump
checked at regular intervals for worn parts.
Pasteurization
With pasteurization, water is heated to kill bacteria,
viruses, cysts and worms. The limited efficiency of the heat
exchange makes pasteurization expensive. Pasteurization
does not leave behind a residual product which continues
to disinfect beyond the immediate treatment period.
Reviewed by
Bob Broz, Extension Water Quality State Specialist, Division of Food
Systems and Bioengineering
extension.missouri.edu eq104
Ultraviolet radiation (UV)
Low-pressure mercury arc lamps produce ultraviolet
light, which has germicidal properties. The radiation kills
or deactivates pathogens. Bacteria are killed with relatively
low amounts of radiation, viruses are more resistant and
cysts and worms are unaffected.
The lamp’s efficiency decreases with age and must be
replaced annually. Color, turbidity and organic impurities
in the water also interfere with transmission of ultraviolet
energy and may reduce efficiency to unsafe levels. Also,
radiation leaves no residual product that continues to
disinfect beyond the treatment period.
Boiling
Boiling water for three minutes kills bacteria, including
disease-causing organisms and giardia cysts. However,
boiling concentrates inorganic impurities such as nitrate
and sulfates. Boiled water also tastes flat because the
carbon dioxide is removed.
Filtration
Filter systems are a relatively simple and effective
way to control a variety of contaminants. These include
mechanical filters, activated carbon filters, oxidizing
filters and neutralizing filters. Filtration systems are
designed for use only on potable water. This means that
your water supply should be clean, uncontaminated and
suitable for drinking.
Mechanical filters (microfiltration)
Mechanical filters remove suspended material from
water, including sand, silt, clay and organic matter. They
do not remove dissolved or very fine particles and are often
used in combination with other treatment equipment.
Filters are commonly made of fabric, fiber, ceramic
or other screening material. Mechanical filters can be
cartridge units, mounted in a single waterline or on a tap,
or tank units, which treat an entire household water supply.
The filters must be serviced periodically.
Activated carbon filters
Activated carbon filters absorb impurities as they pass
through a carbon cartridge. Generally, they are used
to eliminate undesirable odors and tastes and organic
compounds and to remove residual chlorine. Most
inorganic chemicals, metals, microorganisms and nitrates
are not removed by the filters.
Carbon filters also remove some potentially hazardous
contaminants such as radon gas, many dissolved organic
chemicals and trihalomethanes. If low levels of these
contaminants exist, a whole-house unit can be used.
However, these filters are not designed to remove
persistently high levels of these contaminants. When
contamination cannot be eliminated, an alternative water
supply may be the safest solution.
The carbon filter loses its effectiveness as it becomes
saturated with contaminants and must be replaced on a
regular basis. Using the filter longer than its rated lifetime
may cause contaminants to be flushed into the drinking
water. Before purchasing the unit, ask the dealer if the
filter can be replaced, the frequency of replacement, where
replacement filters may be purchased and how much they
cost.
The material in an activated carbon filter provides a
growth surface for certain bacteria. If the filter has not
been used for five or more days, simply run chlorinated
water through the filter for at least 30 seconds before use.
Some manufacturers claim the addition of silver in their
carbon filters will reduce or prevent bacteria growth.
These carbon filters are registered as bacteriostatic by the
United States Environmental Protection Agency (EPA)
due to a requirement by the Federal Insecticide, Fungicide
and Rodenticide Act. The required registration indicates
the filter does not release excessive amounts of silver. The
EPA has not endorsed these methods for reducing bacteria
in the filter or in the water. Furthermore, a bacteriostatic
carbon filter is not adequate to treat water that is
microbially unsafe.
Oxidizing filters
Oxidizing filters remove iron, manganese and hydrogen
sulfide (rotten egg odor). A manganese zeolite-coated filter
causes dissolved iron and manganese to form particles the
filter then traps. These filters are useful in removing iron
if a water softener is not wanted. The filter usually treats
the entire household water supply. Periodically, the filter
must be rinsed with a chemical solution to remove the
accumulated iron and manganese.
Neutralizing filters
Neutralizing filters treat acidic water. The filter treats all
of the home water supply by passing it through limestone
chips or other neutralizing agent. Where acidic water does
occur, it can leach lead, copper or other toxic metals from
household pipes into the water supply.
Two potential problems occur with the filter. First, it
may increase water hardness. Second, acidic water may
intensify any iron problems already present in the water
supply. The filter requires little maintenance except the
need to occasionally replace the limestone chips.
Reverse osmosis
Reverse osmosis pressurizes and passes impure water
through a semi-permeable membrane and removes many
of the impurities, approximately 90 percent free of mineral
and biological contaminants. The quality of the membrane
and the pressure of the water help determine how
effectively the water separates the contaminants.
Reverse osmosis (RO) units remove substantial amounts
of most inorganic chemicals — such as salts, metals and
minerals ­— most microorganisms and many organic
chemicals. They do not effectively remove some organic
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compounds such as nitrate; they will reduce levels
somewhat.
Mechanical filters and activated carbon filters are almost
always used with an RO unit. First, the mechanical filter
removes dirt, sediment and other impurities that clog the
reverse osmosis membrane. The RO unit is installed next.
An activated carbon filter then removes some organic
compounds that pass through the RO unit. Nitrates,
however, will pass through carbon filters.
Reverse osmosis units use large amounts of water.
Typically, about 75 percent or more of the water put into
RO units is discarded with the contaminants. These
systems may not be appropriate for households with
a limited water supply. These units are expensive to
purchase and require regular maintenance. Usually they are
connected to a cooking and drinking line only and installed
under the kitchen sink. Regular testing of the water supply is
necessary to make sure the membrane is intact.
Distillation
Distillation heats water until it vaporizes as steam.
Minerals, bacteria and other substances are left behind
when the steam recondenses into relatively pure water.
Distillers remove bacteria, minerals, trace amounts
of metals, many organic chemicals and nitrate. Some
distillers allow contaminants with boiling points lower
than water, such as some pesticides and volatile solvents, to
vaporize with the water and recondense with the distilled
water. A vented distiller prevents this problem. Note that
distillers also remove beneficial minerals and make water
taste flat or bland.
The distillation process is very slow — daily capacity is
usually between two and five gallons. Approximately five
gallons of tap water are required to produce one gallon of
distilled water. Distillers are relatively expensive. They
require frequent cleaning and may be difficult to keep
clean. Their maintenance requirements and electricity
consumption also should be considered when purchasing a
distiller.
Ion exchange (water softeners)
A common problem of water supplies is hardness, mainly
caused by excess calcium and magnesium. Ion exchange
systems soften hard water by removing the minerals
causing hardness. These hardness minerals may interfere
with the cleaning action of soaps and detergents and cause
scale buildup in hot water pipes, water heaters and fixtures.
The system also effectively removes some iron, manganese
and many heavy metals.
The hard water is pumped through a tank containing
an exchange resin. Sodium on the exchange resin replaces
the hardness minerals. The sodium remains in soluble
form in the softened water. Persons with heart problems
should discuss this issue with a physician who will need to
know the sodium level in the existing household supply of
softened water.
To function properly, the resin tank must be periodically
flushed, or recharged, with a solution of sodium chloride
(salt). Some softeners automatically recharge the tank
either on a regular schedule or when an electronic sensor
detects that the resin needs to be recharged. With automatic
recharge you only need to keep the sodium storage container
filled. Other softeners must be recharged manually and are
usually serviced by water treatment companies.
Purchasing considerations
Before buying a water treatment system, know the quality
of your water supply and if treatment is needed. Consider
the simplest and most economical solution to the problem.
Removing the source of contamination, obtaining a new
source of drinking water, or treating the water with a water
treatment system may be appropriate solutions.
When purchasing a treatment system, ask the following
questions:
• What testing is needed to evaluate my water
supply?
There is no single test to determine if water is safe.
On-site demonstrations are not an accurate indicator
of contaminant levels. Test water for suspected
contaminants through a certified water testing
laboratory.
• Is the system designed to treat the specific water
quality problem?
Check the NSF rating for performance standards of
water-treatment devices.
• How many gallons of treated water does the unit
produce per day?
Is the amount sufficient for your household needs? If
water need is low, purchasing bottled water may be
more cost effective than purchasing water treatment
equipment.
• Is there a sufficient water supply for the
treatment unit to work properly?
Distillation and RO units use large amounts of water.
• How will you know if the unit is not working
properly?
An alarm or indicator light should alert you to a
malfunction.
• What maintenance is required?
All equipment requires maintenance and service.
The more treatment you have, the greater your
responsibility.
• What routine servicing is offered?
Is a service contract available? Unless you are
unusually dedicated, automated and self-monitoring
features or dealer’s service agreements are
recommended to ensure correct operation and high
quality water.
• Is there a warranty?
What does it cover? Make sure any claims about
the performance of the treatment unit are clearly
identified in writing.
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Table 1. Recommended solutions to water quality problems.
1 = First choice or best treatment option
2 = Second choice
3 = Third choice
4 = Fourth choice
Contaminant or problem: Bacteria
1. Locate and remove source of contaminants
2. Alternate water supply
3. Chemical feeder (Continuous disinfection: chlorination)
4. Distillation
Contaminant or problem: Acidity/alkalinity/pH
1. Chemical feeder
1. Neutralizing filter
Contaminant or problem: Sediment/asbestos
1. Sediment filter
2. Reverse osmosis
2. Distillation
Contaminant or problem: Common inorganic chemicals
1. Reverse osmosis
1. Distillation
Contaminant or problem: Heavy metals such as cadmium, chromium, lead, mercury, silver
1. Reverse osmosis
1. Distillation
2. Activated carbon, or a taste and odor, filter is an ideal medium for
bacteria growth. Use only on water supplies that are continuously
disinfected or known to be free of bacteria. Usually a two-stage filter.
Removes small amounts of some contaminants.
2. Chemical contaminant filter. Removes small amounts of some contaminants.
Contaminant or problem: Nitrate/nitrite
1. Locate and remove source of contaminants
2. Alternate water supply
3. Reverse osmosis (Requires semi-permeable membrane, pressure over
60 psi and regular monitoring of salts to ensure effective removal.
Reverse osmosis reduces but does not remove all nitrates.)
3. Distillation
Contaminant or problem: Sodium
1. Alternative water supply
2. Reverse osmosis
2. Distillation
Contaminant or problem: Total dissolved solids (salts)
1. Reverse osmosis
1. Distillation
Contaminant or problem: Iron and manganese
1. Zeolite-ion exchange softening (Iron removal capacity of softening depends on amounts of iron, filter capacity and type of exchange media.
Higher concentrations require use of special iron treatment equipment,
i.e., iron filter).
2. Resin-ion exchange softening. (Iron removal capacity of softening depends on amounts of iron, filter capacity and type of exchange media.
Higher concentrations require use of special iron treatment equipment,
i.e., iron filter.
Contaminant or problem: Hardness
1. Resin-ion exchange softening
2. Zeolite-ion exchange softening
Contaminant or problem: Odor/taste
1. Activated carbon, or a taste and odor, filter is an ideal medium for
bacteria growth. Use only on water supplies that are continuously
disinfected or known to be free of bacteria. Usually a two-stage filter.
Removes small amounts of some contaminants. Iron removal capacity
of softening depends on amounts of iron, filter capacity and type of
exchange media. Higher concentrations require use of special iron
treatment equipment, i.e., iron filter.
1. Chemical contaminant filter. Iron removal capacity of softening depends on amounts of iron, filter capacity and type of exchange media.
Higher concentrations require use of special iron treatment equipment,
i.e., iron filter.
Contaminant or problem: Pesticides/VOCs
1. Alternate water supply
2. Chemical contaminant filter
3. Reverse osmosis
3. Distillation (A vented distiller is necessary for this process.)
4. Activated carbon, or a taste and odor, filter is an ideal medium for
bacteria growth. Use only on water supplies that are continuously
disinfected or known to be free of bacteria. Usually a two-stage filter.
Removes small amounts of some contaminants.
Contaminant or problem: Turbidity
1. Sediment filter
2. Activated carbon, or a taste and odor, filter is an ideal medium for
bacteria growth. Use only on water supplies that are continuously
disinfected or known to be free of bacteria. Usually a two-stage filter.
Removes small amounts of some contaminants.
3. Alternate water supply
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• What is the total cost?
Consider the expected life, purchase price,
installation cost, maintenance cost and operation
cost. Every treatment system has its own advantages
and disadvantages.
• If you rent the equipment, does your agreement
include an option-to-buy provision?
Compare the rental cost to the purchase price and
expected life of the equipment.
Some of the more common treatment methods used to
handle certain contaminants are mentioned in Table 1. This
is a general guide and does not contain all of the potential
treatment techniques or contaminants. The concentration
and combination of various contaminants can have a major
impact on the effectiveness of the treatment method.
References
Shaw, Byron H. and James O. Peterson, Improving Your
Drinking Water Quality, Cooperative Extension
Service, University of Wisconsin-Madison, Madison,
Wisconsin.
Water Quality Association Education Services. 1983.
Water Treatment Fundamentals.
This MU publication — previously named WQ Understanding Home Water
Treatment Systems — was reviewed and adapted for Missouri by Wanda
Eubank, Jerry D. Carpenter and Beverly A. Maltsberger, University of
Missouri, and Nix Anderson, Missouri Department of Health, from “Buying
Home Water Treatment Equipment” by Adel L. Pfeil, Department of
Consumer Sciences and Retailing, Purdue University
ALSO FROM MU EXTENSION PUBLICATIONS
EQ101
EQ102
EQ103
Understanding Your Water Test Report
Bacteria in Drinking Water
Nitrate in Drinking Water
extension.missouri.edu | 800-292-0969
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