There is an impressive array of residential drinking water treatment unit (DWTU) technologies on the market today including adsorptive media, ion exchange, reverse osmosis (RO), ceramic filters, pleated filters, ultraviolet (UV), distillation, reduction oxidation (redox) and others. The NSF DWTU Testing and Certification program addresses these technologies with thousands of DWTU systems and components certified under seven NSF/ANSI standards.
Systems vs. Components
Drinking water treatment systems, as well as components of systems, can be certified under DWTU standards according to the requirements shown in Table 1.
A system is a complete product that is designed to treat residential potable water. Types of systems include plumbed-in, faucet mount, point-of-entry, pour-through and shower filtration systems.
All systems must be tested and certified for at least one contaminant-reduction claim. After all, a DWTU system would be pointless if it did not reduce at least one contaminant from the water. A manufacturer may elect to certify multiple contaminant-reduction claims based on the water treatment technology and claims available in the applicable standards. All pressure-bearing systems are also certified for material safety and structural integrity.
A component is defined as a part or subassembly of a system that must be combined with other components in order to provide treated water. Examples of components include housings, filter cartridges, membranes, faucets, fittings, tubing, valves, storage tanks, etc.
All components are certified for material safety. Pressure-bearing components are also certified for structural integrity. Components are not certified for contaminant-reduction claims because all parts are needed together to know the true system performance.
There are seven technology-specific standards for DWTU products as shown in Table 2. The contaminant-reduction claims that can be made for each type of product vary according to the limitations of the water treatment technology and the claims available in the applicable standard.
Standards 42 and 53 cover the same category of products—POU and POE filtration systems that utilize carbon, mechanical or other filtration. A common question that arises deals with the difference between standards 42 and 53. Standard 42 is for systems that make aesthetic claims such as chlorine reduction, particulate reduction and chloramines reduction. Standard 53 is for systems that make health-related claims such as lead reduction, arsenic reduction, cyst reduction, etc.
Standards 42 and 53 do not mandate which claims must be made. Bacteriostatic effects, however, cannot be the only claim, as this is not a reduction claim but rather a claim that the system does not contribute heterotrophic bacteria to the water. Because components are not certified for claims, any component that is used in systems covered under the scope of 42 and 53 is automatically certified under NSF/ANSI Standard 42.
Standard 55 is specific for UV disinfection units. UV systems certified under this standard are categorized as either Class A or Class B devices based on the UV dosage and sensor. Class A systems are required to have a UV dosage of at least 40 mJ/cm2. They must also include a sensor to indicate if the dosage falls below the minimum. Class B systems must be capable of achieving a dosage of at least 16 mJ/cm2 and are not required to include a sensor.
Standard 58 is for residential POU/RO systems and components. RO systems certified to this standard are required to reduce total dissolved solids (TDS). TDS reduction is also required for distillation systems under Standard 62. Additional health-related contaminant-reduction claims can be certified for products under either standard.
Residential cation exchange water softeners are certified under Standard 44. Standard 44 requires testing for exchange capacity, rinse effectiveness, softening performance and accuracy of the brine system. Radium and barium reduction are optional claims for softeners certified under Standard 44.
Standard 177-Shower Filtration Systems is the most recent DWTU standard. The only contaminant-reduction claim that can be made under 177 is free available chlorine reduction. Also, one important point to note is this standard requires a material safety evaluation instead of the full extraction test required by all other DWTU standards. This difference in approach is due to the fact that shower water is not considered drinking water. The material safety evaluation under standard 177 ensures that materials in contact with shower water do not contain lead as an intentional ingredient and prohibits solvent bonding of plastics.
A system that utilizes multiple treatment technologies may be certified under multiple standards. An example is a system consisting of a carbon filter and a UV lamp. The carbon filter could be certified for claims under standards 42 and 53, whereas the UV technology could be certified for disinfection under Standard 55.
In these cases, the manufacturer must decide which standard(s) to certify against. Often, the selection of standards and contaminant-reduction claims largely boils down to the manufacturer’s product marketing goals.
Understanding the Rationale
Considerable science went into the development of the standards by the Joint Committee on Drinking Water Treatment Units so that the testing requirements and contaminant-reduction claims would logically align with the diverse range of water treatment technologies available on the market.