Household Water Treatment - VCE Publications

Household Water Treatment - VCE Publications
Publication 442-670
Virginia Household Water Quality Program:
Household Water Treatment
Brian Benham, Extension Specialist, Associate Professor, Biological Systems Engineering, Virginia Tech
Erin Ling, Senior Extension Associate, Biological Systems Engineering, Virginia Tech
Private water sources such as wells and springs are not regulated by the U.S. Environmental Protection Agency
(EPA). Although private well construction regulations exist in Virginia, private water supply owners are responsible for
providing maintenance for their water systems, monitoring water quality, and taking the appropriate steps to address
problems, should they arise.
The EPA public drinking water standards are good guidelines for assessing your water quality. “Primary drinking
water standards” apply to contaminants that can adversely affect health and are legally enforceable for public water
systems. “Secondary drinking water standards” are nonregulatory guidelines for contaminants that may cause
nuisance problems such as bad taste, foul odor, or staining.
Testing your water annually and routinely inspecting and maintaining your water supply system will help keep your
water safe. For more information, visit the Virginia Household Water Quality Program website at www.wellwater.bse.
vt.edu.
Introduction
The U.S. Environmental Protection Agency regulates
the allowable level of impurities in public water supplies, but homeowners that rely on private water systems, such as wells, springs, and cisterns, are solely
responsible for the care and maintenance of their water
supplies and for the quality of their water. Those with
private water supplies can use the EPA drinking water
standards as guidelines when assessing their water
quality. When levels of selected impurities in household
water exceed EPA guidelines, they may affect human
health or they may be a nuisance, possibly affecting the
taste, smell, or appearance of the water.
Water is often called the universal solvent. As water
moves under ground or over land, it dissolves a variety
of compounds, including minerals, salts, and organic
compounds. Under certain circumstances, water can
dissolve metals in household plumbing systems, adding impurities to the water. Impurities may also come
from human activities (e.g., misapplying fertilizers or
pesticides), and water can also contain microbiological
organisms.
This publication discusses several types of water treatment devices and, in general terms, the mechanism
each device uses to treat water. No single water treatment device treats all problems, and all devices have
limitations. Once installed, periodic testing of water
samples collected before and after a water treatment
device is recommended to ensure the device is working as intended. A table included at the end of this
publication provides a summary of the common water
treatment devices discussed in this publication, their
primary use, and the maintenance and limitations associated with each device.
The remainder of this publication provides an overview
of common water treatment devices used in the home.
• Filtration: activated carbon filter, sediment filters, media filters, and oxidizing filters.
• Acid water neutralizing filter.
• Water softeners.
• Reverse osmosis.
•Disinfection methods: boiling water, continuous chlorination, and ultraviolet disinfection.
• Distillation.
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and the U.S. Department of Agriculture cooperating. Edwin J. Jones, Director, Virginia Cooperative Extension, Virginia Tech, Blacksburg; Jewel E. Hairston, Administrator, 1890 Extension Program, Virginia State, Petersburg.
VT/442-670/0713/BSE-75P
Filtration
Sediment Filters
Sediment filters are typically used to remove suspended
particles found in water (e.g., sand, silt, clay, and oxidized iron and manganese). Sediment filters remove
impurities by passing the water through a filter material
that is rated or sized according to the smallest particle
it can trap (e.g., 20 microns; a micron is one-millionth
of a meter).
Activated Carbon Filters
Activated carbon filters can be used to treat general
taste and odor problems through the removal of chlorine, some organic compounds (such as some pesticide
residues), radon, and some heavy metals, like lead — if
they are specifically designed to do so. Impurities are
adsorbed, or bound, to the activated carbon as water
flows through the filter (fig. 1).
Cartridge-type filters (fig. 2) are often used in household applications. Typical cartridge filter media types
include pleated paper, cellulose, wound string, and
spun polypropylene (fig. 3).
The effectiveness of an activated carbon filter device
depends on the design of the filter, the type and concentration of the impurities, and the amount of time the
water is in contact with the activated carbon media. To
function properly, these filters must be changed according to the manufacturer’s recommendation. Activated
carbon filters are typically point-of-use (POU) devices,
such as a faucet-mounted filter or pour-through drip
units. Higher capacity point-of-entry (POE) activated
carbon filters are typically only recommend for cases
where volatile organic compounds, radon, or other
impurities should be removed before water enters the
house.
Maintenance involves periodically changing filter cartridges. Sediment filters can be sized and installed to
treat water at the POU, such as a kitchen tap or refrigerator, or higher capacity POE devices can treat all water
entering the house.
Figure 2. A cartridge-type sediment filter.
Figure 1. An activated carbon filter.
Figure 3. Types of cartridge filter material.
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Media Filters
Oxidizing Filter
Media filters (fig. 4) use a graded, coarse (garnet) -tofine (bituminous coal) media to trap suspended particles. In some situations, multiple filters may be needed
to remove suspended particles from the water, with
each subsequent filter trapping smaller and smaller
particles.
Occasionally, impurities must be converted into another
form to be removed more easily. An oxidizing filter is
a POE treatment device that converts dissolved iron,
manganese, or hydrogen sulfide (the gas that produces
the rotten egg odor) into a solid form and then filters
the solid particles from water. The device looks similar
to a media filter or water softener, but the media in the
oxidizing filter is typically a manganese-treated greensand. Other filter media are available depending on the
application.
Maintenance involves periodic backwashing to clean
and refresh the filter media. Depending on the unit,
backwashing may be automatic or manually activated.
Media filters are typically POE devices that treat all
water entering the house.
Maintenance typically involves periodically recharging
the greensand media with an oxidizing agent (typically
potassium permanganate) and backwashing. The potassium permanganate forms a coating that reacts with the
dissolved iron, manganese, or hydrogen sulfide to form
solid particles that are then trapped in the filter media.
The backwashing and recharging frequency depend on
the type and amount of impurities in the water and the
volume of water being treated.
Acid Water Neutralizing Filter
The acidity or alkalinity of water is measured using the
pH scale, which ranges from 1.0 to 14.0. A pH value of
7.0 is neutral, less than 7.0 is acidic, and greater than
7.0 is basic, or alkaline. The EPA-recommended pH
range for public drinking water supplies is between 6.5
and 8.5. While consuming acidic water in itself is not
a health hazard, water that is acidic can be corrosive
and can dissolve metals present in household plumbing — most commonly copper and lead. Consuming
dissolved lead and copper in drinking water can be a
health hazard. Some dissolved metals can also cause
nuisance problems, such as staining of plumbing fixtures or causing water to have a bitter or metallic taste.
Figure 4. A media filter.
An acid water neutralizing filter is a relatively simple
treatment device that raises the pH of water by adding
a neutralizing material, which decreases the likelihood
that the water will dissolve metal pipes and fixtures.
The most common type of neutralizing filter is the tank
type, in which water flows through a neutralizing media
composed of calcium carbonate (limestone), crushed
oyster shells, marble chips, or synthetic magnesium
oxide material (fig. 5). As the water flows through the
neutralizing media, the media is dissolved and the pH
of the water increases.
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Water Softeners
Maintenance involves periodically adding more neutralizing media. How frequently the media must be
replenished depends on the pH and the volume of water
being treated. Using an acid water neutralizing filter
will likely increase the hardness of the water. Depending on the amount of hardness added, a water softener
may also be needed. Acid water neutralizing filters are
typically POE devices that treat all of the water entering the house.
“Hard” water is water with high levels of minerals (calcium and magnesium) that it acquires as it
flows through and dissolves natural geologic deposits — usually limestone or other carbonate rock. The
most common way to remove hardness, or to “soften”
household water, is a cation-exchange water softener.
Water exceeding about 7 to 8 grains per gallon (gpg) or
approximately 120 milligrams per liter (mg/L) of hardness may interfere with the cleaning action of soaps
and detergents and may cause mineral deposits (scale)
on dishes, appliances, and plumbing fixtures.
Cation-exchange water softeners work by replacing hard water ions (calcium and magnesium, which
are positively charged ions, or cations) with soft ions
(sodium, also positively charged). This ion exchange
occurs as water flows through the ion-exchange resin,
which is stored in the softener tank (the center tank in
fig. 6).
Water softener maintenance involves routinely adding
sodium pellets to a brine tank typically located adjacent
to the softener tank (fig. 6). These pellets typically come
in 40-pound bags. The brine solution is used to periodically regenerate the ion-exchange resin by adding
sodium cations. Resin regeneration may be automatic,
semiautomatic, or manual — depending on the system.
The most efficient water softeners use a flowmeter to
determine regeneration cycle frequency. Some water
treatment companies offer maintenance programs for
water treatment devices, including softeners.
POE water softener devices can be installed to treat all
water used in the house or only the water that flows to
the hot water heater. Water used for drinking, cooking,
toilets, and outdoor use should not normally be softened. Water softeners can also be used to remove small
amounts of iron and manganese (with combined concentrations less than 5 mg/L).
Figure 5. An acid water neutralizing filter.
If a water softener is being used to remove iron, all
water entering the house should be treated. Because
water softeners are designed to meet specific needs, it
is critical to have a water sample analyzed by a certified
lab before purchasing any water treatment device.
Water softeners add sodium (salt) to water. Individuals
on restricted-sodium diets should consult a physician
before consuming softened water.
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Figure 6. A water softener with schematic showing the ion-exchange process.
Reverse Osmosis
Disinfection Methods
Reverse osmosis (RO) units are typically POU devices
capable of reducing the concentration of most dissolved
and suspended inorganic impurities, but they are not
typically recommended to remove organic impurities,
including bacteria. With RO systems (fig. 7), impurities
are removed as water is forced through a semipermeable membrane with microscopic holes that are large
enough to allow water molecules to pass through but
small enough to block most dissolved and suspended
impurities. Ten to 20 percent of the water entering the
RO system exits as treated water. The other 80 to 90
percent is wastewater that is diverted to a drain.
Boiling Water
Various types of disinfection methods can be used to
treat microbiologically unsafe water. Perhaps the most
straightforward disinfection method is boiling. Disinfection via boiling requires a vigorous or roiling boil
for at least one minute. While boiling water is an effective disinfection method for small quantities of water,
boiling is not an efficient means of disinfecting water
for use in an entire house. Typical POE disinfection
methods for household water disinfection include continuous chlorination and ultraviolet (UV) radiation.
Care must be taken not to foul (clog) the RO membrane. Hard water can quickly foul an RO membrane.
A sediment prefilter is frequently used to pretreat the
water before it enters the RO membrane unit. An activated carbon postfilter may be used after the RO membrane unit (fig. 8). In some modular RO systems, these
components may be included in a single unit.
Continuous Chlorination
Continuous chlorination systems use a chemical meter
to add chlorine to the water supply system to kill bacteria. With a sufficiently high chlorine concentration
and adequate contact time, chlorine will kill bacteria
and certain viruses, but it will not kill Giardia or Cryptosporidium — two parasites associated with surface
water contamination of wells and springs.
Maintenance involves periodically replacing the RO
membrane and any associated filters in accordance
with the manufacturer’s recommendations.
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Figure 7. A reverse osmosis (RO) schematic.
Figure 8. Typical, under-sink, reverse osmosis (RO) system components.
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The effectiveness of chlorine depends on the concentration of chlorine in the water, the amount of time the
chlorine is in contact with the water prior to use (contact time), the water temperature, the pH of the water,
and the characteristics of other impurities in addition to
the amount of bacteria in the water supply. Because the
groundwater may contain several impurities that can
be oxidized by the addition of chlorine (e.g., organic
matter other than the bacteria, dissolved metals such as
iron and manganese, or hydrogen sulfide), the amount
of chlorine needed to treat a given water supply must
be determined on a case-by-case basis. A sediment or
media filter may be required following a chlorination
system to filter out oxidized impurities. If chlorine taste
or odor is an issue, an activated carbon filter may be
needed to remove residual chlorine from the treated
water.
UV lamp must also be kept clean. Some units have
integrated wipers that are used to periodically clean the
quartz sleeve that houses the UV lamp (fig. 9).
Finally, the concentration of bacteria in the water
supply can also affect UV radiation treatment effectiveness. If the water supply contains large concentrations of bacteria (more than 1,000 total coliforms per
100 milliliters or more than 100 fecal coliforms per
100 milliliters), an alternative disinfection method is
recommended.
Maintenance of continuous chlorination systems
involves ensuring that the metering device is feeding
the correct amount of chlorine to the system and ensuring that there is a sufficient supply of chlorine (solution, powder, or tablets) available. Closely following
the manufacturer’s operating instructions is critical to
ensuring that continuous chlorination devices function
properly.
Figure 9. An ultraviolet (UV) radiation disinfection unit.
Ultraviolet Radiation
Using ultraviolet radiation for continuous disinfection
is fairly common. UV radiation disrupts the bacteria’s
genetic material, making reproduction impossible.
While UV radiation is effective for bacteria and viruses,
it is less effective for Giardia or Cryptosporidium. In
a typical household UV system, untreated water enters
the UV unit and is exposed to the UV radiation as it
flows through the device (fig. 9).
Distillation
Distillation is perhaps the oldest form of water treatment. Distillation units boil water to create steam,
which is then condensed and collected as distilled water
(fig. 10). Distillation reduces the concentration of metals, minerals, and some organic chemicals. Impurities
remain in the evaporation chamber (where the heating element is located). Because distillation removes
minerals that are naturally present in water that impart
taste, distilled water can have a very “flat” taste.
To effectively disinfect a water supply, the UV lamp
must emit UV light at the correct intensity. The age
of the lamp and the characteristics of the water being
treated both affect intensity. UV lamps weaken over
time and must be changed according to the manufacturer’s recommendations.
Some distillation units may allow undesirable impurities that have a boiling point lower than water (e.g.,
some pesticides and volatile solvents) to vaporize and
recondense, which means they remain in the distilled
water. Some distillation units have a volatile gas vent
that releases these impurities into the atmosphere. Distillation also works to disinfect water by killing microorganisms and bacteria.
Water that is cloudy or contains sediment will limit UV
light penetration. As a result, the UV disinfection system is typically the last device in a household water
treatment system, preceded by other devices designed
to filter or otherwise clarify the water supply. To ensure
effective light penetration, the housing containing the
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Summary
It is critical to have a water sample analyzed by an
independent, certified lab and to consult a professional
before purchasing any water treatment equipment.
Keep in mind that no single water treatment device
treats all problems, and all devices have limitations.
In many cases, there are multiple household water
quality issues that must be addressed. In these situations, a combination or system of treatment devices
may be needed. The water treatment system designer
must consider the type and concentration of the various
impurities to be removed and the intended use for the
treated water (e.g., drinking and cooking versus laundry, bathing, or flushing toilets). The initial cost as well
as the operating costs must be considered when selecting water treatment equipment.
One should also be aware of the type and amount of
maintenance needed to ensure the equipment functions
properly. Consider getting two or three opinions from
different suppliers before making a decision to purchase a water treatment device or system.
Figure 10. A distillation unit.
Finally, any water treatment equipment being considered should be certified by an independent third party,
like NSF International (www.nsf.org). All water treatment devices must be properly maintained to work as
intended. Periodic water quality testing of samples collected before (upstream) and after (downstream) any
water treatment device is recommended to ensure it is
working properly.
Distillation units are typically POU devices that treat
comparatively small volumes of water. Countertop
units typically yield less than 3 to 4 gallons of water
per day. Larger units can yield 8 to 12 gallons per day.
Home distillation units tend to be energy intensive,
requiring about 800 watts of electricity to distill 1 quart
of water.
Periodic maintenance and cleaning of the distillation
unit is required because minerals and other impurities
accumulate in the evaporation chamber and can potentially interfere with the operation. Hard water can be
especially problematic with distillation units because a
mineral scale can form in the evaporation chamber and
on the heating element, increasing operating costs. As
with any treatment device, follow the manufacturer’s
maintenance recommendations.
Additional Information
Remember, the manufacturer’s manual is the best
resource for maintenance instructions for your water
treatment device. For additional information on water
quality and treatment, contact your local Virginia
Cooperative Extension office.
For more drinking water quality information, see these
Virginia Cooperative Extension websites:
• Virginia Household Water Quality Program –
www.wellwater.bse.vt.edu/resources.php
• Virginia Cooperative Extension – http://pubs.ext.
vt.edu/category/home-water-quality.html
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Table 1. Quick reference to common water treatment devices.
Device
Primary use
Maintenance and limitations
Activated carbon filter
Removes chlorine and some organics.
Used to address general taste and odor
issues. Can be used to remove some
metals if designed to do so.
Does not remove bacteria or nitrate. Requires
periodic replacement of activated carbon
media.
Sediment filter
Removes suspended particles that
cause turbidity (e.g., sand, silt, clay,
oxidized iron, manganese, and sulfur).
Requires periodic cartridge replacement.
Media filter
Removes suspended particles that
cause turbidity (e.g., sand, silt, clay,
oxidized iron, manganese, and sulfur).
Requires periodic backwashing to clean and
refresh the media.
Oxidizing filter
Filters out oxidized iron, manganese,
and hydrogen sulfide.
Requires periodic backwashing and
regeneration of filter media.
Acid water neutralizing
filter
Raises pH, reducing water
corrosiveness.
May increase water hardness. Requires
periodic addition of neutralizing media.
Water softener
Reduces water hardness, removing
dissolved calcium and magnesium.
Improves cleaning action of soaps, etc.
Prevents scale deposits in pipes and
appliances.
Requires periodic addition of salt to brine
tank. Requires periodic backwashing and
regeneration of softener resin.
Reverse osmosis
Reduces the concentration of dissolved
and suspended impurities in water.
Typically yields 10-20% treated water by
volume. Requires storage for treated water.
Hard water can foul RO membrane. Must
periodically replace RO membrane and any
associated filters.
Continuous chlorination
Disinfects water supply by adding
chlorine.
Must ensure sufficient chlorine concentration
and contact time to achieve disinfection. Must
maintain chlorine supply and ensure chlorinemetering device is working properly. Sediment
and activated carbon filters may be required.
UV disinfection
Disinfects water supply by exposing
bacteria to UV radiation.
May require sediment filter upstream of UV
unit to reduce turbidity. Must periodically
replace UV bulb.
Distillation
Removes most impurities and disinfects
by boiling water, then condensing
steam.
Yields limited volume of treated water. May
be expensive to operate due to energy cost.
Treated water may have “flat” taste. Hard
water can interfere with operation.
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Acknowledgements
References
This publication was adapted from “Household Water
Treatment,” Virginia Cooperative Extension publication 356-481, by K. Parrott, B. Ross, and J. Woodard,
1999. The authors wish to thank the following individuals who reviewed this publication: Sharon Skipton,
extension water quality educator, Nebraska Cooperative Extension; Renee Boyer, food science and technology specialist, Virginia Cooperative Extension; John
Thompson, agriculture and natural resources agent,
VCE Fluvanna County Office; and Dawn Barnes, family and consumer sciences agent, VCE Floyd County
Office.
Clemens, Stephanie, and Bryan Swistock. 2007. Water
Facts No. 18: Tips for Buying Water Treatment
Equipment. Penn State. College of Agricultural
Sciences, Cooperative Extension. School of Forest
Resources. Code XH0022.
Connecticut Department of Health. 2009. Publication
No. 19: Questions to Ask When Purchasing Water
Treatment Equipment for Your Home. Environmental Health Section, Private Well Program. Private
Drinking Water in Connecticut Series. Connecticut
Department of Public Health.
Dvorak, B. I., G. Prasai, S. Skipton, and W. Woldt.
2007. Drinking Water: Iron and Manganese. University of Nebraska-Lincoln Extension. Institute of
Agriculture and Natural Resources. Nebguide Publication G1714. www.ianrpubs.unl.edu/epublic/live/
g1714/build/g1714.pdf.
Midwest Plan Service. 1992. Private Water Systems
Handbook. Iowa State University. MWPS-14.
Ames, Iowa.
PlumbingSupply.com. 1995. “Acid Neutralizer Installation Information.” Web page. www.plumbingsupply.com/neutralinstall.html.
Wagenet, L., K. Mancl, and M. Sailus. 1995. Home
Water Treatment. Natural Resource, Agriculture,
and Engineering Service. Cornell University Cooperative Extension. Publication NRAES-48.
The Virginia Household Water Quality Program, offered through Virginia Cooperative Extension, periodically conducts
county-based household water sampling clinics where you can learn about the quality of your water supply, proper
water supply system maintenance, and, if needed, possible water treatment options. Please contact your local Extension
office or visit www.wellwater.bse.vt.edu for more information.
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