January 2001: Volume 43, Number 1
Drinking Water Treatment Standards -- The Process of Certification
by Shannon Murphy
Editor's Note: Charts accompanying this article are available only in the .pdf version. See end of article for hyperlink.
With all the different requirements and regulations that drinking water products have
these days, it’s easy for regulators, users and even manufacturers to be unclear about
requirements of the ANSI/NSF drinking water treatment unit (DWTU) Standards, not to
mention what stating “Certified to ANSI/NSF Standard” means regarding the
functionality of the certified product for federal and state regulators, retailers, food
service and consumer acceptance.
Upon further review
There are currently six DWTU standards. Standards 42 and 53 cover carbon and
mechanical filtration type systems. Standard 42 includes aesthetic claims like chlorine,
taste and odor and bacteriostatic. Standard 53 covers health claims like lead, VOC’s,
MTBE and cyst. Standard 44 covers water softeners, testing for items like hardness
reduction, efficiency rating as well as radium and barium reduction.
Standard 55 covers ultraviolet systems, testing for items like disinfection Class A and B.
Class A systems are defined as systems meeting the requirements to disinfect and/or
remove microorganisms from contaminated water, including a 6 log reduction for
bacteria and a 4 log reduction for viruses. These systems aren't designed to treat water
that has an obvious contamination source, like raw sewage. Class B systems are designed
for supplemental bactericidal treatment of treated and disinfected public drinking water
or other drinking water, which has been deemed acceptable by a local health agency.
Standard 58 is for the certification of reverse osmosis (RO) units. RO systems have the
added capability of a “treatment train” effect. These systems typically consist of a
prefilter (or series of prefilters), the RO membrane and a final filter. Standard 58 covers
reduction claims such as fluoride, hexavalent and trivalent chromium, total dissolved
solids (TDS) and nitrate/nitrite reduction. Finally, there's Standard 62, which covers the
certification of distillation systems and reduction claims like mercury, nitrate/nitrite,
arsenic and microbiological performance.
While there are differences between the standards regarding the type of systems they
represent, there's also much similarity between them. All standards are broken down into
seven separate sections with the essential testing and evaluation in Section 4-7.
Section 4 covers materials in contact with drinking water. Each material that’s in contact
with drinking water must be reviewed to ensue nothing detrimental is leaching out of the
device into the drinking water. Formulation information for each wetted part is required
with each material and requires reference to the Code of Federal Regulations Title 21
(CFR 21), which is a codification of the general and permanent rules published in the
Federal Register by the executive departments and agencies of the federal government.
Once all component formulation information has been received, a toxicologist with a
doctorate or master’s degree reviews the ingredient information of the components and
determines what analytes need to be examined during extraction testing. All analytes are
selected based on detail formulation review of all materials in contact with drinking
water. The exposure test is a conservative “in product” test, which is conducted over a
three-day period. Extraction water is collected and analyzed for contaminants determined
by the toxicologist during the formulation review. Results are forwarded to the
toxicologist in order to compare them against current allowable levels.
In addition to current allowable levels, the standards refer to Advisory Concentrations,
which are set by the DWTU Joint Committee (see "Water Matters: Standards on the
Move From Arsenic to Total THMs," WC&P, November 1999)—the body that oversees
development and maintenance of the standards—as limits lower than the regulated levels.
The thought is that since these are water treatment devices intended to reduce specific
contaminants from the water, they shouldn’t add any level of certain contaminants. A
good example of this is lead. The U.S. Environmental Protection Agency currently has
set the lead maximum drinking water level (MDWL) at 15 parts per billion (ppb). The
DWTU joint committee has set an advisory concentration level at 5 ppb. With lead such a
closely watched contaminant, it was determined standards should emphasize the
elimination of lead a filter leaches into the drinking water. Thus, the joint committee
identified a number of contaminants of high priority and set these levels.
Product lines are capable of sharing test data across standards. For example, a product
certified to Standard 42 would already meet the material extraction and structural
integrity requirements of Standard 53 in the event the manufacturer wanted to add a
health claim to their Standard 42 listed product. It’s always better to provide your
certification body information on all products intended to be certified for the certification
agency to determine the fastest, least expensive approach to certification.
Section 5 covers design and construction. In short, this section covers testing of the unit
in order to ensure it will function properly when installed correctly. Under Standards
42/53, this includes hydrostatic pressure, burst pressure and cyclic pressure testing.
Depending upon the system and rated pressure of the unit, each system may need some if
not all three tests. Standard 58 is a bit more detailed, covering items like flow control,
reject water connections, drinking fountain outlets, performance indication and storage
tank capacity. Additionally, there are specific requirements for nitrate/nitrite and arsenic
reduction claims. Nitrate/nitrite systems must have either a monitor on the product water
stream or provide an analysis kit with the system. Arsenic claims must indicate that these
systems be used on water supplies maintaining detectable residual-free chlorine since this
is how the system is evaluated under the standard.
Some, but not all
Where each system must meet the specific requirements for both material extraction and
design and construction, reduction claims covered under Section 6 are pick and choose.
In short, the system isn’t required to meet all reduction claims covered under Section 6.
Many systems are designed for specific end purposes. With this in mind, manufacturers
certify their product for certain claims in order to target specific end users. Systems
designed for chlorine and/or taste and odor removal can be excellent systems
manufactured at reduced cost and easily certified. On the other hand, systems
manufactured for additional claims like MTBE, TTHM and/or cyst reduction need
additional engineering and, thus, may require additional testing in for certification.
Allowing manufacturers to pick and choose individual reduction claims enables
companies to target specific user niches in the most economical manner.
Instruction and information
The most subjective section of the standard is the instruction and information section.
Within this section, the standard covers specific requirements for product literature in
order to ensure clear, non-misleading literature for the consumers. These requirements
include items like installation, operation and maintenance instruction, data plate and
replacement component literature requirements. Additionally, the standards reference a
performance data sheet, which provides a quick summary of all system requirements and
reduction testing information regarding that system. The performance data sheet was
developed by the joint committee in order to provide the consumer details about various
water treatment devices prior to purchase. This enables the consumer to make a more
educated and satisfying purchase.
Products certified to any of the six DWTU standards are required to pass material
extraction testing. DWTU extraction protocol requires conditioning as per the
manufacturer’s use instructions, followed by the three-day, 24-hour extraction protocol
(three samples each with 24-hour exposure to the system). This differs from ANSI/NSF
Standard 61 where many of the sections have an extended conditioning period. An
example of this is in Standard 61, Section 8, which covers mechanical plumbing devices
like pumps, valves and tanks. Under this section, a product is provided a 14-day
conditioning period during which there are 10 water changes.
Following this conditioning period, there’s an additional two-day condition followed by
the sample collection. This extended conditioning was integrated into the standard since
installation of many of the products into a system or home occurs before the home is
occupied. Additionally, many of these products have an extended life of 10 years or more
within the potable water system. On the other hand, DWTU products usually are
designed to last a specific period of time before the user is directed to replace the filter
Additional differences include whole product pressurized extraction testing under DWTU
standards. Here, the complete unit is hooked up to a system under line pressure and
extraction tested. Standard 61 exposure protocol isn’t under line pressure. Additionally,
DWTU materials are required to be CFR 21 compliant, where Standard 61 materials
Under the requirements of the standards, components are capable of being certified for
material extraction and—if having a pressure bearing component—for structural
integrity. There are already a number of component manufacturers certified to Standards
42 and 58. The use of certified components in a system will significantly reduce the cost
and time to get a complete system certified since much of the work has already been
completed. When in doubt, always inquire about the acceptance of a listed Standard 42,
58 or 61 component or material in a final product. Frequently this can be a quick cost and
time saver for system certification.
About the author
Shannon Murphy is operations manager of the Drinking Water Treatment Unit program
at NSF International in Ann Arbor, Mich. His bachelor's degree from Concordia
University in Montreal, Canada, is in biology. His master's degree from Wayne State
University in Detroit is in biology with an emphasis on limnology. Murphy can be
contacted at (800) 673-6275, (734) 769-0109 (fax) or email: email@example.com
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