The Wide, Wide World of Residential Water Treatment Product Testing

Technology-specific testing methods in relation to the American National Standards

Consumers today can choose from an incredible array of options for treating their household water. From water softeners to faucet-mount filters, from ultraviolet (UV) to reverse osmosis (RO), from pour-through pitchers to shower filters, the variety is huge.

This wide-ranging choice in technologies has led to the development of seven different American National Standards for establishing their contaminant reduction performance (see Table 1). This development of technology-specific test methods makes logical sense – a water softener functions very differently from a faucet mount filter, so the two products should be tested differently.

This article will focus on the variety in technology-specific testing methods found in these seven standards, and the associated laboratory apparatus utilized to implement these test methods. If you have ever wondered how manufacturers claims are verified for various products, this is your chance to find out.

Filter Testing

The first standards adopted were Standards 42 and 53, for filtration products. These standards include test methods for both pour-through, gravity-fed filters (such as pitcher filters), and for filters connected to plumbing.

For the pour-through, gravity-fed filters, the test method is relatively simple. Water is processed in batches manually by lab technicians. There has been a discussion regarding whether it is appropriate to use a controlled slow feed of influent water, such that a continuous flow through the filter is achieved. This approach saves a great deal on the labor of processing batches manually; however, it misses out on some very real issues related to actual consumer usage. When a consumer pours a pitcher, the filter is tipped. This tipping can disrupt the media bed, and can introduce air into the bed. This disruption could potentially affect contaminant reduction, so it must be addressed when testing products in the laboratory.

For plumbed-in filters, the method is not so simple. The pressure must be controlled very tightly. For Standard 42 testing, the flow rate must be controlled tightly. For Standard 53, the flow rate achieved by the product at the specified test pressure, with no constriction on the inlet or outlet, is used. To simulate turning faucets on and off as the filter is used, on/off cycling of flow according to prescribed times is required.

Testing of chemical reduction claims is based on the manufacturer’s capacity rating for the filter. Samples of the influent and effluent must be collected at specific percentages of this capacity rating. In contrast, mechanical reduction claims, such as particulate reduction and cyst reduction, require testing until the filter is plugged to a 75% reduction in flow rate from the initial, clean filter flow rate at the start of the test. Sample points are dictated by the change in flow rate of the filter as it clogs. As a further complication, cyst reduction testing requires introduction of clean water, water containing cysts, and water containing a special clogging dust to be introduced in various alternating patterns throughout the test.

In addition, the water used to introduce the contaminants must fall within specified parameters of pH, total dissolved solids, total organic carbon, hardness, alkalinity, and so forth, depending on the specific test being conducted. For some tests, tap water adjusted to meet the requirements is specified in the Standards. For others, reverse osmosis treated, deionized water must be used, with specific amounts of reagents added in to build up the required water chemistry.

Shower filters fit into this category, with the added requirement that they must be tested with hot water.

All of these requirements lead to the design of special “test rigs” to enable laboratories to conduct testing to the Standards. There are two basic types of test rigs – batch, or tank rigs; and injection rigs. Batch rigs utilize large tanks of contaminant challenge water that are pre-mixed to contain contaminants. Injection rigs send water throughout a manifold, with specific contaminants injected at the test stand. Batch rigs are easier to design and operate, but injection rigs save space and, when properly operated, save labor. Batch rigs are easy to visualize, as they consist of a tank with mixing apparatus, some solenoid valves and timers.

RO Testing

Testing of RO systems is in many ways similar to testing filters, but there are differences. For one, the water chemistry is different, which causes complications when operating injection test rigs. Second, the inlet pressure is lower. Third, the sample points are not based on a capacity rating or plugging of the system, but are rather time-based throughout a one-week testing period. And fourth, some of the samples must be a specific volume based on the production rate of the RO system.

Softener Testing

Softener testing has some similarities to filter testing for chemical reduction. However, capabilities to measure pressure drop are required, as well as accurate balances for determining the accuracy of the brine system. Online hardness monitors to determine the endpoint of a capacity test can make this testing run much more smoothly. Finally, many softeners operate at high flow rates, so the laboratory water supply and plumbing must be designed with this capability.

Distiller Testing

Distiller testing is somewhat similar to RO testing in that the test period is one week. If microbiological claims are to be tested, the laboratory must have microbiological handling and analysis capabilities in addition to the typical chemical analysis required.

UV Testing

UV testing requires microbiological handling and analysis capabilities, as well as chemical analysis capabilities. Additionally, many point-of-entry UV systems flow at high flow rates, so test rigs must be designed with large plumbing and pumps in order to accommodate these products. UV systems must be tested with addition of parahydroxybenzoic acid (PHBA) to reduce the UV transmittance of the water, so the laboratory must be able to control addition of the PHBA to the test rig.

A Huge Investment

Obviously, all of these different types of test apparatus, coupled with the associated analytical instrumentation required to determine concentrations of various test water requirements and contaminants, adds up to a huge investment for testing laboratories. Because of this investment, some testing laboratories choose to, or must work with an array of subcontractors. This is a way for those laboratories to reduce the level of investment required to provide a broad scope of services.

This arrangement can work well, as long as relationships are maintained through clear communication of scheduling and QC requirements, and close contact to ensure that needs are being met.

Other laboratories have chosen to invest in a “one-stop-shop” approach, utilizing few if any subcontractors to provide service. This approach can work well for overall consistency, timeliness and project management, but comes with the added investment risk that demands higher test volumes.

The overall structure of a testing service provider is a differentiating factor that manufacturers must consider when choosing a partner to provide product evaluation and testing. Whatever the structure of the testing service provider, the manufacturer must be satisfied that their partner can deliver the project turnaround, quality, scope of services, reliability, and ultimately, the value that they need.

“They Just Run Lead Through It”

I once overheard some lay persons discussing verification of claims on a faucet mount filter. “How do they know it actually reduces lead?” mused one. Another answered, “They just run lead through it.” On one level, this is correct. There is no magic here – lead reduction claims are indeed verified by introducing water contaminated with lead into the product, and verifying that the concentration of lead on the effluent side is reduced. But, as with many areas of life, the devil is in the details. The concentration of lead must be carefully controlled, along with the pH, hardness, alkalinity, and so forth, of the test water. The inlet pressure must be carefully regulated. On and off cycling of flow through the filter must be timed. Samples must be carefully collected at prescribed intervals. Testing must be conducted at two pHs.

At the end of the day, I would say there is quite a bit more to it than just running lead through the filter. wqp

Rick Andrew is the technical manager of the Drinking Water Treatment Units Program of NSF for more than three years. He has been with NSF International for more than six years, working with certification of residential drinking water products. His previous experience was in the area of analytical and environmental chemistry consulting. Andrew is a member of the Editorial Advisory Board of Water Quality Products. He has a BA in chemistry and an MBA from the University of Michigan. He can be reached at 800.NSF.MARK, or by e-mail at

Leave A Comment

  • Web page addresses and e-mail addresses turn into links automatically.
  • Allowed HTML tags: <a> <em> <strong> <cite> <code> <ul> <ol> <li> <dl> <dt> <dd>
  • Lines and paragraphs break automatically.

More information about formatting options

By submitting this form, you accept the Mollom privacy policy.