By Rick Andrew

As the water treatment market in the United States matures, consumers are searching for more integrated water treatment solutions. Likewise, American consumers seek new appliances that have more features than the appliances they owned previously. A good indication of these trends includes several categories of integrated water treatment products which have emerged in recent years:

  • Filter faucets, which combine a filtered water pathway in addition to an unfiltered water pathway in the same kitchen faucet;
  • water-cooler based treatment systems, which add a variety of water treatment capabilities to water coolers including filtration, reverse osmosis and UV;
  • refrigerator filters, which provide cooled filtered water and ice made from filtered water on demand from the refrigerator.

These examples highlight the combined functionality and increase in product features that Americans crave, as well as the integrated solutions that water treatment manufacturers have provided in response to this market trend.

Each of these integrated water treatment products has its own nuances in terms of certification, each for different reasons. There is overlapping scope with drinking water treatment unit (DWTU) and non-DWTU standards in the cases of filter faucets and water-cooler based water treatment systems. With refrigerator filters, the nuances are more subtle logistical issues involved in testing a system that is contained within a refrigerator. This article will examine those logistical issues with testing of refrigerator filters, and the recent revisions to NSF/ANSI 53 that have been incorporated to address those issues.

Unique products
Refrigerator filters are unique because they are encased within an appliance that is primarily used for a different function. These filters are typically manufactured by familiar water treatment industry suppliers, and then integrated into the refrigerator by the appliance manufacturer. This integration can be complicated, because the refrigerator usually has a coil of tubing that serves to chill the water, a valve that delivers water to the water dispenser and ice maker, a flow controller and a water dispenser and ice maker. The filter is a system within this environment that provides the desired water treatment.
There are several specific issues that must be addressed in order to establish conformance of the filter system to NSF/ANSI Standard 53, given the scenario described above.

  • The tubing, water valve and flow controller contained within the refrigerator will have an impact on line pressure drop and therefore on flow rate through the filter system.
  • The flow controller is external to the filter system.
  • There are two pathways for filtered water: through the water dispenser and through the ice maker.

NSF and the DWTU Joint Committee recognized that this set of circumstances required new Standard language to be developed. NSF drafted a ballot proposal, which was recently approved and incorporated into Standard 53.

New Standard 53 language for refrigerator filters
This new language specifically addresses the unique aspects of typical refrigerator filter system manufacturing, as described above.

Standard 53 requires that chemical reduction testing be conducted at the maximum flow rate attainable with a 60 psig dynamic influent challenge pressure. For this reason, integral flow controllers are required for products that depend on a specific flow rate for their performance.

Because refrigerator filters typically do not have integral flow controllers, a new section 6.3.2 has been

added that allows flow controllers for refrigerator filters to be external to the system. Integral flow controllers are required for other filtration systems because of the risk of higher flow rates in the field than those tested for conformance to the Standard, if the system is installed without the flow controller. However, refrigerator filters are constructed such that they cannot be used unless they are installed in a refrigerator, which has the required flow controller within it. There is no risk of refrigerator filter systems being used by consumers without the flow controller, as there is with other types of filtration systems.

The fact that flow controllers are typically included in the refrigerator, external to the refrigerator filter system, creates an issue when conducting contaminant reduction testing. In order to incorporate the flow controller, the entire refrigerator would need to be plumbed in to the test stand in the laboratory.

Plumbing in an entire refrigerator when conducting contaminant reduction testing would also take into account the impact on line pressure drop and flow rate of the tubing, water valve, and flow controller contained within the refrigerator.

However, utilizing entire refrigerators is impractical. They are large and take up an excessive amount of space in the laboratory. They are expensive to produce and ship. The water pathway becomes contaminated after chemical reduction testing has been conducted, so the refrigerator is not acceptable for usage after testing is completed without extensive reworking. Because of these impracticalities, additional new language has been added to the standard.

According to this new language, the flow rate for contaminant reduction testing of refrigerator filters may be controlled to the maximum flow rate attainable through the entire refrigerator and filter water flow path with a 60 psig dynamic influent challenge pressure. If the filter supplies water to both a water dispenser and an ice maker, the flow rate through both must be measured in order to determine which allows the maximum flow rate attainable.

In practical terms, this means that prior to conducting chemical reduction testing, a complete refrigerator with filter system is plumbed (in) to the test stand. The maximum flow rate attainable through the entire refrigerator and filtered water flow path with a 60 psig dynamic influent challenge pressure is measured. When the contaminant reduction testing is conducted, refrigerators are not required to be used. The filter systems may be plumbed directly to the test stand and challenged with a 60 psig dynamic influent challenge pressure. When tested this way, without the refrigerator flow controllers, the flow rate through the filter systems is controlled using needle valves (See Figure 1) to be equal to or greater than the measured flow rate. These needle valves are available in different sizes (1/4”, 1/2”, 3/4”, etc.), and are adjustable by turning a dial. This dial is a fine adjustment that opens and closes the valve, allowing for precise control of flow rate.

By conducting the testing in this manner, only one refrigerator is needed to establish the flow rate. The refrigerator is not contaminated because no contaminants are introduced when the flow rate is measured. The testing may then be conducted at or above this established flow rate by testing filter systems only and using needle valves to control the flow. This approach provides a simple, economical, convenient, practical and conservative solution to a complex testing issue.

Standards evolve to address marketplace changes
When I was a child, the refrigerator did two things: it kept food cold and it had a small freezer at the top. Some readers may even remember the days of the ice box! Today, a high end refrigerator keeps food cold, has a freezer, alarms when the door is left open, provides humidity controlled vegetable storage, has electronic programmable temperature controls and delivers filtered water and ice made from filtered water.

These developments in refrigeration and new applications for water treatment have necessitated the development of new DWTU standards language. Fortunately, these standards are living documents that are in a constant state of improvement by the hard-working Joint Committee and volunteer Task Groups. They are constantly being revised to address new developments, applications and technologies. The emergence of refrigerator water filtration systems serves as a good case study of how the DWTU standards evolve to address new applications.

Next time you visit an appliance or home improvement store, visit the refrigerator aisle. Take a look at the variety and prevalence of water filtration systems included with refrigerators. You will have a new appreciation for the issues involved in testing these filter systems and the development work on the DWTU standards that was required to help facilitate their testing.

About the author
Rick Andrew has been with NSF International for over five years, working with certification of residential drinking water products. He has been the Technical Manager of the Drinking Water Treatment Units Program for over two years. 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]


Comments are closed.