By Rick Andrew

The NSF/ANSI Drinking Water Treatment Unit (DWTU) Standards are different from many other product standards in that not all requirements spelled out in them must be met for a given product to conform to them. For example, there are no products that meet all of the requirements of NSF/ANSI 53, Drinking water treatment units—Health effects. There are well over 50 contaminant reduction claims possible under this standard, some of which require very specific product design and engineering that may not be compatible with achieving other claims under the standard.

The fact that not all requirements are met can understandably cause confusion for those studying the standards and for those examining products that are certified to the standards. Questions arise, such as exactly which requirements, if any, must be met for products to conform to the standards? Which requirements are optional? How can users or purchasers determine the scope of certification given the optional nature of certain requirements in the standards?

The goal of this column is to shed some light on the requirements of the NSF/ANSI DWTU Standards, to help alleviate the confusion that arises regarding the scope of certification for products. See Figure 1 for a quick general overview of the types of requirements that various products must meet to conform to these standards.

Material safety evaluations
The common denominator of all products conforming to the NSF/ANSI DWTU Standards is a material safety evaluation. Components and systems alike must be manufactured using materials appropriate to the end use of water treatment. For all products except shower filters, this involves a formulation review for all materials in contact with water and an extraction test to make sure that no contaminants leach above acceptable concentrations.

Structural integrity requirements
All of the NSF/ANSI DWTU Standards require that pressure-bearing components must meet structural integrity test requirements. Structural integrity evaluations may include cyclic, hydrostatic and/or burst testing, depending on the specific product and Standard.

Certified systems must make claims
All complete water treatment systems conforming to the NSF/ANSI DWTU Standards must make at least one claim. There is not much point in a water treatment system that does not actually perform treatment!
Because different water treatment technologies have different capabilities and are used for different purposes, the specific claims required vary by standard. See Figure 2 for a quick overview of the required claims by standard and by water treatment technology.

Reverse osmosis (RO) systems have contaminant reduction capabilities based on the use of a RO membrane. One of the basic characteristics of these membranes is rejection of ions dissolved in water. Because this characteristic is common to all RO systems, all of them must meet requirements for reduction of total dissolved solids in order to conform to the NSF/ANSI 58.

Similarly, properly functioning distillers vaporize and condense water vapor, leaving behind dissolved solids. Therefore, all distillers must be capable of reducing total dissolved solids to conform to NSF/ANSI 62.

Water softeners universally remove hardness, so all of them must pass a softening performance test. A second test is required to establish their softening capacity at various salt dosages. Finally, their brine systems must accurately deliver the proper amount of salt, so there are requirements for an evaluation of the brine delivery system calibration.

Shower filters are designed to reduce free available chlorine. They must be able to do so under test conditions involving hot water to the capacity claimed by the manufacturer.

Ultraviolet (UV) systems are designed to disinfect water. These systems are required to deliver specific UV dosages under specific test conditions, to establish their ability to control nuisance organisms in potable water supplies (Class B) or their ability to disinfect visually clear but potentially contaminated water supplies (Class A).

Filter systems are more open-ended
Filter systems are a broad category of product. They may include and utilize such media as activated carbon, metals sorbents, redox media or they may utilize mechanical filtration such as ceramic or other technologies. They may consist of loose, granular media or they may be carbon block type. Because of the variability in the nature, configuration, materials and medias of these products, there is a wide variety of capabilities and limitations.

Because of this variability, there are no specific claims required under NSF/ANSI 42 and NSF/ANSI 53. In fact, these standards actually cover the same products and are applied to those products based on the wide variety of claims made. Those claims can be broadly categorized as aesthetic or not related to reduction of contaminants that can affect human health and health-related claims. NSF/ANSI 42 addresses aesthetic claims such as reduction of chlorine and particulate matter, whereas its sister standard, NSF/ANSI 53, covers health-related claims such as reduction of lead or volatile organic contaminants (VOCs).

Although no specific claims are required under Standards 42 and 53, at least one claim is required. And there is one limitation under Standard 42 that bacteriostatic effects may not be the only claim made on a system. If the only function of a filter is that it does not contribute to heterotrophic bacteria populations in the water supply, there is not much value in that filter. So, a filter system claiming bacteriostatic effects must also make other claims in order to meet the requirements of NSF/ANSI 42.

Certified claims information requirements
The Joint Committee on Drinking Water Treatment Units considered the necessity of communicating the exact scope of certification for DWTUs. As such, the standards require that the specific contaminant reduction claims must be identified on the product data plate, in the installation, operation and maintenance instructions and in some cases on the replacement element packaging. These information requirements help ensure that the scope of certification is accurately communicated to consumers.

Complicated, but rational
As with the technologies and products themselves, certification of residential water treatment components and systems is a complex topic. Fortunately, there is a tremendous amount of science and logic behind the certification requirements. Once you understand the science and logic of the technologies and standards, the various claims and other requirements make sense. Next time someone asks you how it is possible that two different filters can be certified to Standard 53, yet only one is certified for cyst reduction, you will be able to answer the question and enlighten the inquirer.

About the author
Rick Andrew is the Operations Manager of the NSF Drinking Water Treatment Units Program. Prior to joining NSF, his previous experience was in the area of analytical and environmental chemistry consulting. Andrew has a bachelor’s degree in chemistry and an MBA from the University of Michigan. He can be reached at 1-800-NSF-MARK or email: [email protected].


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