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 cartridge.
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 aren’t.
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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