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Introduction
Although most drinking
water in the United States is considered safe, there is increasing concern about
the quality of drinking water as more and more pollutants are found in
groundwater supplies. Worry about the possible health problems resulting from
these contaminants is causing consumers to wonder what they can do to ensure the
quality of their own water supply. The most strongly recommended and best
solutions to the problem of a contaminated water source are either ending the
practices causing degradation of the water source, or changing water sources.
These options may not always be practical or may take months or years for
completion. In the mean time, other solutions may be necessary. Installation of
a home water treatment system may be one viable alternative for people with
contaminated drinking water. It should be recognized that home water treatment
is considered only a temporary solution. Treatment systems can be quite
expensive, require regular monitoring and maintenance and no one system can be
used for all contaminants. They may also become less effective if the degree or
type of contamination changes over time. As a result, authorities recommend
that bottled water be used for drinking and cooking purposes. This bulletin
will provide a guide for consumers who want to know about home water treatment
systems. The first step for a homeowner or renter with a suspected water quality
problem is to obtain a chemical analysis of the water from a local health
department or private laboratory. Public health professionals can aid in
interpreting the results. It is important to remember that the presence of a
contaminant does not always mean that treatment of the water is needed. A water
quality professional will use the chemical analysis to determine which, if any,
water treatment system is appropriate. Many water quality problems are of
esthetic rather than health concern; e.g. bad odor or taste. Although these
types of problems are important and may also be remedied using home water
treatment systems, this bulletin will focus on contaminants which may lead to
adverse health effects.
There are a variety of water
treatment processes that are available to the homeowner. The systems differ in
the types of chemicals removed, location within the home, and operating and
maintenance requirements. Two broad categories of home water treatment units are
point-of-use (POU) and point-of-entry (POE) systems. POU systems are installed
near the point of use, normally in the kitchen at the end of a faucet, plumbed
in-line under the sink, or placed on a countertop. These systems typically treat
the 3 to 5 gallons per day which the average family uses for drinking and
cooking. POE units are larger, more expensive, usually placed in the basement
and treat water as it enters the home, generally excluding water to outdoor
taps. POU or POE treatment systems are most economical if they are sized and
operated to supply treated water only in quantities needed. POE devices offer
the best protection from both esthetic and health related contaminants.
However, POU devices are generally cheaper. POE devices are often preferred when
iron or hardness is present. The presence of these compounds can discolor
fixtures and clothes, or lead to excessive buildup of scale in water piping.
There are several processes available for home water purification. These include
activated carbon, ion exchange, reverse osmosis, distillation, chemical
oxidation and ultraviolet radiation treatment. These processes purify water by
removing contaminants or transforming them into less objectionable compounds. A
major disadvantage of all the processes is that verification of performance can
usually only be determined by expensive chemical analysis. Therefore, filter
replacement or maintenance may not be performed when necessary. If the filter is
not functioning properly, the water may contain unacceptable levels of
contaminants. It is also not possible to know with certainty the degree of
contaminant removal unless appropriate water testing has been performed.
Home
treatment systems are not regulated by federal, state or local laws. Regulatory
authorities generally consider home systems temporary solutions. This is because
no system is capable of removing all possible contaminants and the potential for
malfunction or improper maintenance is too great, in some cases, for these to be
considered long term solutions. There is also no way for governmental agencies
to monitor their performance in each home. Thus, to best protect public health,
authorities recommend that permanent solutions, such as a new water source or
clean up of the old source be developed. Certification of treatment products is
available to manufacturers through independent testing laboratories, one of the
most prominent being the National Sanitation Foundation (NSF). Results from NSF
tests provide good measures of the effectiveness of devices designed to treat
water for both esthetetic and health reasons. Those interested in particular
systems can contact the NSF to determine if these devices have certified for the
use intended. The Water Quality Association (WQA), a self-governing body of
manufacturers and distributors, offers voluntary validation programs and
advertising guidelines to their members. However, certification, registration or
validation may be misleading. For example, manufacturers may be certified by an
organization which used test conditions ideal for contaminant removal, but not
representative of home conditions.
TREATMENT
PROCESSES
Activated Carbon
Activated carbon (AC) is
commonly used to remove organic contaminants from water. Common organic
contaminants are pesticides, industrial solvents such as trichloroethylene, and
components of gasoline such as benzene. The contaminants interact with the large
surface area of the AC by a process called adsorption. AC has also proven
effective for removal of radon and many natural organic compounds which can
cause unpleasant tastes and odors. AC treatment systems use replaceable
cartridges containing granular or powdered block carbon. Cartridges with the
most carbon remove the most contaminants and last the longest, thus increasing
the time between cartridge replacement. Tests show that under-the-sink models
have more carbon, greater convenience and better performance than faucet and
countertop models. Cartridge life expectancy can be maximized, and replacement
costs minimized, with systems that allow dispensing of unfiltered water at the
tap for purposes other than drinking or cooking. The following considerations
are important when purchasing AC filters;
1. Contaminant removal efficiency,
2. Ease of cartridge replacement
3. Effectiveness of attached sediment filters, which prevent cartridge clogging
4. Amount of pressure loss at the faucet caused by the filter
5. Risks associated with possible bacterial growth on AC.
Ion Exchange
Ion exchange
works by exchanging a compound in the water for a chemical on the filter resin.
It is effective for treatment of ions or charged contaminants. Most inorganic
compounds can be removed by ion exchange, however, most common organic compounds
cannot effectively be removed. Ion exchange is most commonly used to remove
compounds which are of esthetic rather than health concern. Water softeners are
the best known examples of ion exchange systems. Water softeners soften water by
removal of calcium and magnesium which make water hard. These hardness ions in
water are exchanged for the sodium ions attached to the resin surface. The
water softener will no longer be effective when all sodium ions on the resin
have been replaced by hardness ions. At this time, it is necessary to recharge
the resin with sodium. This is accomplished by flushing the resin with high
concentrations of salt (sodium chloride). There may be some health risks
associated with consuming the exchanged sodium ions from home water softeners
for people with high blood pressure and heart disease. These people should check
with health professionals to determine if their maximum allowable intake of
sodium will be exceeded by using a home water softerner. Ion exchange systems
have also been developed for removing nonhardness chemical ions, such as nitrate
and metals. Recharging the resins, in these cases, can only be done at special
facilities, making this form of treatment expensive.
Reverse Osmosis
Reverse osmosis (RO) is a membrane separation process, employing
a very thin membrane which allows water through but not various undesirable
chemicals. RO membranes can remove all major types of contaminants including
bacteria, metals, nitrate, and organics. However, there are some organic
chemicals that may not be removed very efficiently. A RO system works by
applying a high pressure to the contaminated water, forcing pure water through
the membrane. Pure water collects on one side of the membrane while pollutants
accumulate on the other side. The pollutants are periodically flushed to the
sewer or septic system. RO membranes should last at least one year before
replacement is needed. The typical RO system consists of: a sediment filter
which protects the RO membrane, the RO module, activated carbon (AC) prefilters
to remove chlorine for chlorine sensitive membranes, AC postfilters to remove
some organics, a tank for water storage, and provisions for waste flow to
drains. RO units are generally located at the point of use because of the small
volume of water treated. They are typically located under the sink or on the
countertop. Pretreatment with water softeners is often recommended for
extremely hard water. Regular replacement of pre and postfilters is required.
An important factor to consider regarding RO is the large volume of water that
is wasted. This can be on the order of 25-60 gallons per day, depending on the
amount of treated water needed and the pressure drop across the
membrane.
Distillation
Distillation relies on evaporation to
accomplish water purification. It removes inorganic compounds, such as lead and
nitrate, and some organics which do not easily evaporate and so are left behind
in the distillation process. During distillation the water is heated to form
steam. The steam is cooled and condenses to form purified water. Unevaporated
contaminants are left behind and periodically flushed to the septic or sewer
system. Distillers are POU systems and may be countertop, wall mounted, or
placed on carts. Systems can be manual, partially or fully automated. Some
models can separate volatile organic compounds before distillation. An advantage
of distillation for use on water supplies which have not been chlorinated is
that disinfection occurs during boiling. Care must be taken to avoid
recontamination of the condensed purified water in the storage container by
bacteria. Problems associated with distillation include loss of beneficial
minerals from water and water that may taste flat. Operating costs may be higher
than other forms of home treatment. Production of heat from a distiller may be
beneficial in the winter but a disadvantage in the summer.
Chemical Oxidation
Chemical oxidation works by chemically changing the pollutant
to a compound that is less objectionable. Chemical oxidants also act as
disinfectants by killing bacteria and viruses. Chlorine is a common oxidant
which is added to most public water supplies for disinfection purposes. There
are several strong oxidizers which may be practical for home water treatment of
a bacteria contaminated water supply. These include hypochlorite or hypochlorous
acid and hypobromite or hypobromous acid. They are available in powder or liquid
form. Automatic feeders are used to add the chemicals directly to water in the
pipes. They can be either point of use or point of entry systems. Adequate
contact time is essential to ensure disinfection. Chlorinated oxidants can
impart an unpleasant taste to the water and may produce potentially harmful
chlorinated organics (trihalomethanes) by reacting with natural organic
materials present in the water. Ozone is another chemical oxidant. It can
destroy bacteria in drinking water without creating the taste and odor problems
common with chlorine. In addition, many organic compounds can be partially or
completely oxidixed by ozone with no formation of chlorinated compounds. The
effectiveness of an oxidant can be influenced by water temperature, acidity,
concentration of oxidant, contact time with the oxidant prior to water use, and
other factors. Pretreatment may be required for turbid
water.
Ultraviolet Radiation
Ultraviolet (UV) radiation
disinfects drinking water by killing microorganisms. Sufficient levels of UV
radiation must be applied or it may merely retard growth or impede reproduction
of bacteria and viruses, rather than destroy these organisms. UV systems are
placed directly into water lines at convenient locations for POU or POE
treatment. UV should be the final treatment if it is combined with other
technologies. The other devices can remove dissolved and undissolved materials
which inhibit the disinfection process and UV can kill any bacteria left in the
system. A UV disinfection system consists of a prefilter for sediment removal
in addition to a UV-emitting lamp. Good designs should provide:
1. Maintenance with easy tube and lamp
removal
2. Flow rates that provide adequate contact time between radiation
and bacteria
3. Easy visual inspection of the lamp and tube.
The primary advantage of UV treatment
is that no disinfecting chemicals are added. Taste and odor problems are less
likely to arise when chlorine is not added. However, chlorine provides residual
disinfecting power downstream of the application point while UV provides no such
residual.
Bottled or Bulk Water
Bottled or bulk water may be a
viable alternative to home water treatment if it is needed only for a short
period of time. It may be necessary during the time the homeowner is pursuing a
new source of water or installing a home water treatment system. Bottled
water is regulated as a food by the Food and Drug Administration (FDA). The FDA
concerns itself mostly with sanitation and labeling but is also responsible for
ensuring that bottlers comply with Primary and Secondary Drinking Water
Standards. Only those bottlers working in more than one state are regulated by
the FDA. In Michigan, the Department of Public Health (MDPH) regulates bottled
water sources and the Department of Agriculture (MDA) regulates labeling and
quality. Bulk water, delivered to the home and stored in large tanks, is
available in some Michigan communities. This may be more convenient for some
people.
SUMMARY
There are many strategies for dealing with a
water contamination term solution since no one system can work for all
contamination problems and none are maintenance free. The homeowner or renter
should take the time to learn about the water source and the treatment systems
available to ensure an appropriate resolution of the problem.
BUYERS
CHECKLIST
1. Have a water analysis performed by a qualified laboratory.
2. Discuss your results with health professionals
to
obtain their recommendations.
3. Research different products on the
market, comparing initial and operating/maintenance costs, contaminant removal efficiency, company reputation, and service
record.
4. Read manufacturer's claims and warranties carefully to make
sure that the capacity and life expectancy meet your needs.
5. Understand the operation and maintenance requirements when the unit is
installed. Find out where to obtain replacement filters and who will service
the equipment when problems arise.
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Reprinted from The Michigan State University
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