At Clearly Filtered, we believe clean water should come with complete confidence. That’s why our filters undergo rigorous testing and third-party certification so you know they meet (and exceed) the highest industry standards. Keep reading to discover how testing and certification work and why it matters for your water.

Testing is the process of evaluating a filter’s performance under controlled conditions to verify its ability to meet specific water safety standards or defined outcomes.

In the context of water filtration, testing involves passing water “spiked” with controlled amounts of added contaminants through to confirm the filter actually reduces those specific contaminants and to measure specific reduction rates. Simply put, it means adding contaminants to water and measuring how well the filter removes them.

Key elements of testing include:

• Accuracy: Testing ensures that results are consistent and repeatable.

• Scope: Filters are tested using set concentrations of specific contaminants (such as lead, mercury, PFAS, pesticides, pharmaceuticals, and more).

• Performance Definitions: Testing follows established protocols, such as those defined by certifying bodies (ANSI and NSF) or specific performance goals.

Certification, on the other hand, is the process by which an accredited certification body (e.g., NSF, WQA, IAPMO) verifies a filter’s performance claims meet specific performance, safety, or quality standards established by a standard-setting organization (such as ANSI and NSF). 

Certification provides added third-party reassurance by confirming that a filter has been tested using credible, standardized protocols. Certified products aren’t just tested once; they’re subject to ongoing auditing and retesting to ensure they continue to meet the standards over time.

Key elements of certification include: 

• Independent Verification: Certification bodies maintain strict protocols while administering testing to ensure results are consistent and credible.

• Documentation: Certified filters earn a certificate or seal, indicating compliance with set standards.  

• Ongoing Compliance: Certification is not a one-time event; it requires regular retesting and facility audits. 

• Consumer Trust: Certification provides assurance that the filter performs as advertised and meets established safety standards.

Testing offers maximum flexibility because manufacturers can choose what to test for—even contaminants not included in current certification standards. This approach allows companies to evaluate their products beyond the limits of any one certification, giving a more complete picture of a filter’s performance.

Certification, in contrast, is a formal process that requires independent performance testing to specific, pre-defined standards. Certification often  includes other requirements as well, such as material safety evaluations. When a filter passes certification testing, it earns the official seal of approval from an accredited organization—signaling to consumers that the product meets established standards.

We often aim for both. 

By pursuing both independent testing and certification testing through accredited labs, companies can provide consumers with valuable insights into the capabilities and benefits of their products. We often test our products beyond certification standards to, help ensure every drop of water is as clean as possible.

Bottom line? 

Certification is like running an official marathon—you must follow a set course and meet the rules to get an official time and medal. Testing, however, is like training on your own terms. You can run farther, faster, or on different terrain. You’re still proving your ability, but not within the strict limits of the race.

The National Sanitation Foundation (NSF) works with the American National Standards Institute (ANSI) to create standards that ensure water treatment devices—like filters, distillers, and shower systems—are composed of non-toxic materials and reliably and adequately target specific contaminants. 

The NSF/ANSI standards are industry benchmarks for water filtration performance. 

NSF/ANSI certification ensures third-party verification of contaminant reduction, filter performance, and material safety. Certification doesn’t have to come from NSF itself—any properly accredited organization can certify to these standards.

Key Certifying Bodies:

• NSF International: Creates protocols and certifies filters to NSF/ANSI standards, including material safety, structural integrity, and contaminant reduction.

• Water Quality Association: WQA’s Gold Seal is the oldest third-party testing and certification program in the water treatment industry. The easily recognized Gold Seal mark lets consumers know that filters have been tested to industry standards and meet NSF/ANSI standards.

International Association of Plumbing & Mechanical Officials: IAPMO’s research lab (IAPMO R&T) certifies drinking water treatment devices. Similar to WQA, IAPMO R&T tests filters to NSF/ANSI standards and issues their own seals that indicate filters were certified by accredited labs.

When evaluating water filters, it’s important to understand the difference between testing to NSF/ANSI standards and obtaining NSF certification.  

Testing to NSF/ANSI standards means an independent lab evaluates a filter’s performance using NSF/ANSI testing protocols. This process measures contaminant reduction, flow rate, and durability under controlled conditions, but it does not result in official NSF certification.

NSF certification, on the other hand, goes beyond filter testing. It includes additional steps such as material safety reviews, structural integrity testing, and manufacturing facility audits to verify consistent filter quality–all done by an entity accredited to certify. If a filter meets all requirements, it earns the NSF seal, signifying official certification.

Our bestselling Filtered Water Pitcher is certified to the following NSF/ANSI standards:

• NSF Certified to NSF/ANSI 42: Focuses on improving the taste, smell, and appearance of your water by reducing contaminants like chlorine.

• NSF Certified to NSF/ANSI 372: Verifies that filter materials meet the definition of "lead-free.""

• WQA Certified to NSF/ANSI 42 and NSF/ANSI 372: WQA (Water Quality Association) is a separate accredited certifying body that tested our filter independently and confirmed the same results as NSF — giving you two organizations standing behind the same claims.

While NSF develops standards, ANSI officially approves them. All certifying bodies—like NSF, WQA, and IAPMO—must be ANSI-accredited to ensure consistency and impartiality. 

As you can see, our flagship filtered water pitcher proudly carries multiple certifications—a reflection of the high standards we uphold across our entire product line. Every Clearly Filtered system undergoes the same rigorous testing, far exceeding what’s typical for conventional store-bought systems.

Unlike ordinary filters, all of our products are powered by Affinity® Filtration Technology—our advanced filtration technology designed to target harmful contaminants while preserving the healthy minerals your body needs.

Our filters are independently tested and proven to reduce up to 99.99% of over 365 contaminants—far beyond what current NSF/ANSI standards require. To achieve and verify this level of performance, we partner with advanced laboratories capable of testing across a broader spectrum of contaminants than standard certifications cover.

While certification confirms a filter meets specific standards, testing without certification allows us to go even further: evaluating additional contaminants, collecting more data, and proving reduction performance where no official certification exists.

When it comes to water filtration, lab quality makes all the difference. Expertise, accreditation, testing processes, and reliability vary widely. 

That’s why it’s critical we choose the right lab so that every filter is tested to meet the highest standards for performance and safety. 

How We Chose the Right Lab

1. PFAS Testing: We exceed standard requirements by working with labs equipped to verify our filters target PFAS and other real-world contaminants effectively.

2. NSF/ANSI Expertise: Testing to NSF/ANSI standards is essential. Our lab partners ensure our filters meet rigorous industry benchmarks with accurate, reliable results.

3. Beyond Certification: Our lab partners test our filters under challenging conditions, using a wide range of contaminants, to go beyond standard protocols to ensure reliable performance in day-to-day life.

By partnering with the most qualified labs, we ensure that every Clearly Filtered system delivers exceptional water filtration—backed by science and verified by industry-leading experts.

Our Lab Partners

We publish results from two independent accredited labs: IAPMO and NSF. These organizations are recognized across the industry for rigorous, unbiased testing — which is why we trust them to verify our filtration performance.

​The NSF/ANSI certification process for water treatment systems is a comprehensive procedure designed to ensure filters meet stringent safety and performance standards. Here's an overview of the key steps involved:​

This process ensures filters meet high standards for safety, performance, and reliability.

When evaluating water filters, test results can be presented in several ways:

• Max Reduction Rate: The highest level of contaminant reduction measured across the filter’s full lifespan.

• Average Reduction Rate: The reduction levels averaged across all data points throughout the testing period.

• End-of-Life Performance: How well the filter performs as it nears the end of its usable life.

Many brands focus solely on max reduction rates to highlight the best possible performance. While impressive, these numbers don’t always reflect real-world performance over time.

In the past, we followed industry norms and shared our max reduction rates. However, to provide a more accurate view of our filter performance, we've shifted to sharing average reduction rates based on all data points collected throughout testing. 

This gives a more realistic picture of how our filters perform over the life of the product and helps you make more informed decisions about when to replace them. (Remember, filter performance can vary based on your local water conditions, and not all listed contaminants may be present in your water).

Lab Conditions: Testing is conducted in controlled environments using challenge water—clean water spiked with isolated contaminants at specific concentrations. The results represent removal rates under ideal conditions.

Real-World Conditions: Real-world water, on the other hand, will never start as simple as challenge water. Because it comes from public water supplies, it already contains a mix of contaminants, sediment, and organic material that can affect filter performance. While lab results provide a consistent baseline, they don't capture the complexity of real-world water.

Clearly Filtered uses certified lab testing to ensure filter reliability, while also helping customers understand how factors like water source, usage, and regional quality can affect performance.

Our filters are tested and certified to perform effectively with tap water commonly found in most homes. We openly share our lab test results so you can understand how your filter performs, know when it might be time for a replacement, and have complete confidence in every sip.

To help you stay on top of filter maintenance, tap here for our recommended filter change schedule. Keep in mind: factors like hard or highly contaminated tap water, reduced water flow, heavy usage, and changes in taste may signal it’s time to change your filter sooner than the lab lifespan suggests. In other words, if your water has more to capture than typical municipal water, your filter is working hard to capture them all. As a result, the flow may slow down sooner than expected—a sign the filter is doing its job.

Want to know what’s in your water? Tap here to enter your zip code into our tap water database. You’ll get a full report on the contaminants in your area’s water supply, along with personalized filter recommendations—so you can trust every drop.