Article Summary: NSF/ANSI 55 is the standard for ultraviolet (UV) drinking water treatment systems. Class A systems are certified for treatment of microbiologically contaminated water; Class B systems provide supplemental treatment of drinking water already considered safe. Check the exact model, certification class, and rated flow before choosing a system.
NSF/ANSI 55 UV Water Systems: Class A vs. Class B
What Does NSF Certification Mean for a Water Treatment Product?
An NSF/ANSI standard sets requirements for a particular kind of water treatment product. An independent certification organization tests a specific product against that standard and lists the claims it has verified. NSF is one certification organization; other organizations may certify products to the same NSF/ANSI standard.
Check the exact claim. “Certified to NSF/ANSI 42” does not mean a filter reduces every substance covered by Standard 42. Likewise, “tested to NSF standards” does not mean the same thing as “certified to NSF/ANSI 55.” Look up the exact model in the certification organization’s product listing.
Common NSF/ANSI Standards for Water Treatment
NSF/ANSI standards cover different types of water treatment products and different performance claims. The standard number helps identify what a product has been evaluated for, but certification does not mean the product addresses every contaminant or water-quality concern covered by that standard.
Always check the exact product model and the specific claims included in its certification listing.
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| Standard | What It Addresses | Common Product Type |
| NSF/ANSI 42 | Aesthetic water-quality claims such as chlorine, taste and odor reduction | |
| NSF/ANSI 53 | Specific contaminant-reduction claims associated with health effects, such as lead or cyst reduction when included in the product listing | Carbon and specialty filters |
| NSF/ANSI 55 | Ultraviolet drinking water treatment systems, including Class A and Class B systems | |
| NSF/ANSI 58 | Reverse osmosis drinking water treatment systems and RO components | RO systems and membranes |
| NSF/ANSI 401 | Reduction of specific emerging compounds or incidental contaminants included in a product's certification | Specialty filtration products |
Important: Certification applies to the exact model and claims shown in the certification listing. A certified filter, membrane or other component does not automatically make the complete water treatment system certified to the same standard.
Importance of NSF Certification
Certification gives shoppers independent evidence for the claims shown in a product’s listing. It helps you compare the intended use and rated performance of specific models. The certification is most useful when you verify the model number and follow the manufacturer’s installation and maintenance instructions.
You can also look up a specific model in the NSF certification database to confirm the standard and exact reduction or performance claims included in its listing.
What Is NSF/ANSI 42 Certification?
NSF/ANSI 42 applies to aesthetic water-quality claims. These are characteristics such as chlorine taste and odor that can affect how water tastes or smells.
Carbon filters are commonly certified under NSF/ANSI 42. However, certification is specific to the claims shown for the exact product. An NSF/ANSI 42 certification should not be interpreted to mean that a filter reduces every substance addressed by the standard.
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Omnipure K2533 Carbon Filter
The Omnipure K2533 inline granular activated carbon filter is certified to NSF/ANSI 42 for chlorine reduction and taste and odor reduction. It is commonly used as an inline filter or RO postfilter.
What Is NSF/ANSI 53 Certification?
NSF/ANSI 53 applies to specific contaminant-reduction claims associated with health effects. This differs from NSF/ANSI 42, which focuses primarily on aesthetic concerns such as chlorine taste and odor.
A product certified under NSF/ANSI 53 is evaluated only for the specific reduction claims shown in its certification listing. Two products certified under the same standard may have very different certified claims.
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Omnipure Q5615 Carbon Block Filter
The Omnipure Q5615 is a useful example because the same filter carries certified claims under multiple NSF/ANSI standards:
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NSF/ANSI 42: chlorine reduction and taste and odor reduction
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NSF/ANSI 53: lead reduction and cyst reduction
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NSF/ANSI 401: microplastics reduction
This is why shoppers should check both the NSF/ANSI standard number and the specific certified claim rather than looking only for an NSF certification mark.
What Is NSF/ANSI 58 Certification?
NSF/ANSI 58 applies to reverse osmosis drinking water treatment systems and RO components. The standard includes requirements related to areas such as materials, structural integrity and reverse osmosis performance.
Certification may apply to a complete RO system or to an individual component such as an RO membrane. That distinction is important when comparing products.
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AXEON 200360 RO Membrane
The AXEON 200360 TFC-1812-75 is a 75 GPD reverse osmosis membrane certified to NSF/ANSI 58.
This is an example of a certified RO component. Installing an NSF/ANSI 58-certified membrane does not automatically make every complete RO system in which it is installed NSF/ANSI 58 certified.
What Is NSF/ANSI 401 Certification?
NSF/ANSI 401 addresses certified reduction claims for specific emerging compounds or incidental contaminants.
As with other NSF/ANSI standards, certification applies only to the claims listed for the exact product.
For example, the Omnipure Q5615 is certified under NSF/ANSI 401 specifically for microplastics reduction.
System Certification vs. Component Certification
A water treatment system may contain filters, membranes, housings, pumps, tanks or other components that carry their own certifications.
Certification of an individual component does not automatically certify the complete assembled system.
When reviewing a certification claim, check:
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The manufacturer
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The exact model number
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The NSF/ANSI standard
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The specific certified claims
Whether the certification applies to a complete system or an individual component
What Is NSF/ANSI 55?
NSF/ANSI 55 covers ultraviolet drinking water treatment systems. It defines two classes with different intended uses: Class A for treatment of microbiologically contaminated water and Class B for supplemental treatment of drinking water already considered safe. The standard and class tell you more than a general “UV certified” claim does.
What Is NSF/ANSI 55 Class A Certification?
NSF/ANSI 55 Class A systems are intended to treat microbiologically contaminated water. Class A has a minimum UV dose of 40 mJ/cm² at its certified operating conditions. A certified model’s sensor, alert, flow control, water quality limits, and maintenance instructions are part of selecting and operating it correctly. Check its listing and manual for the exact requirements and certified flow rate.
For a private well, test the water and identify any treatment needed before UV. UV performance depends on water clarity and proper installation. A UV system does not replace water testing or treatment of contaminants outside its certified claims.
Top-Selling NSF/ANSI 55 Class A UV Systems
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VIQUA PRO10
NSF/ANSI 55 Class A
10 GPM Certified Flow
Certified to NSF/ANSI Standard 55 Class A, the Pro10 is a Point of Entry (POE) ultraviolet system designed to treat up to 10 gpm@40mJ/cm² and features an amalgam lamp that provides higher strength as well as up to 2 years of lamp life.
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Luminor LBH6-251A
NSF/ANSI 55 Class A
7.9 GPM Certified Flow
Certified to NSF/ANSI Standard 55 Class A, the Luminor LBH6-251A is a point-of-entry UV system rated for 7.9 GPM at 40 mJ/cm². It features a high-output UV lamp, 316L stainless steel chamber, and UV intensity sensor that continuously monitors UV performance, with a full-color controller displaying lamp life, system status, and alerts.
What Is NSF/ANSI 55 Class B Certification?
NSF/ANSI 55 Class B systems are for supplemental treatment of drinking water that has already been treated or determined safe. They are intended to reduce non-disease-causing bacteria. Class B is not a substitute for a Class A system when the water supply may be microbiologically contaminated. Compare the exact model’s certification listing and rated flow before buying.
Top-Selling NSF/ANSI 55 Class B UV Systems
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VIQUA VH200-V
NSF/ANSI 55 Class B
7.8 GPM Rated Flow
Certified to NSF/ANSI Standard 55 Class B, the VIQUA VH200-V is a point-of-entry UV system with a rated flow of 7.8 GPM. It is designed for supplemental treatment of drinking water and features a lamp-life countdown controller, 35-watt UV lamp, and 100–240V, 50–60Hz operation.
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Luminor LB5-101B
NSF/ANSI 55 Class B
13 GPM Rated Flow
Certified to NSF/ANSI Standard 55 Class B, the Luminor LB5-101B is a point-of-entry UV system with a certified flow of 13 GPM at 16 mJ/cm². Designed for supplemental treatment of water that is already treated, it features a 39-watt UV lamp, polished 304 stainless steel chamber, and a full-color LCD controller displaying lamp life, diagnostics, fault messages, and service reminders.
Class A vs. Class B UV Systems: Side by Side
Class A vs Class B: Key Differences
| Compare | Class A | Class B |
| Intended water | May be microbiologically contaminated | Already treated or determined safe to drink |
| Minimum UV dose | 40 mJ/cm² | 16 mJ/cm² |
| Shopper’s first check | Water test, certified flow, installation limits | Existing water supply, certified flow, intended use |
Why Can a Certified UV Flow Rate Be Lower?
UV dose depends partly on how quickly water passes the lamp and how well UV light travels through the water. A certified rating can therefore differ from a standard model’s advertised flow. For example, The Luminor LBH6-251A product page states a 7.9 GPM Class A certified flow; it compares that with 25 GPM for the standard LBH6-251 under different dose and UV transmittance conditions. Size the certified model using its certified flow, and leave its supplied flow restrictor in place.
NSF-Certified Water Treatment Product Examples
Different NSF/ANSI standards apply to different treatment technologies and performance claims. These ESP Water Products examples show why it is important to match the standard to the treatment goal.
Other NSF Certified Products
| If You're Looking For | Relevant Standard | Product Example |
| Chlorine taste and odor reduction | NSF/ANSI 42 | |
| Lead and cyst reduction | NSF/ANSI 53 | |
| UV water treatment — Class A | NSF/ANSI 55 | |
| UV water treatment — Class B | NSF/ANSI 55 | |
| Reverse osmosis membrane | NSF/ANSI 58 | |
| Microplastics reduction | NSF/ANSI 401 |
Remember: A product certified to an NSF/ANSI standard is certified only for the specific claims included in its listing. Always verify the exact manufacturer, model number, standard and certified claim.
What Does NSF Certification Not Tell You?
Certification does not mean a system reduces every contaminant. NSF/ANSI 55 is a UV treatment standard; it does not, by itself, certify removal of lead, chemicals, or hardness. A listing applies to the exact model and specified claims. Performance also depends on correct installation, water conditions, certified flow, and maintenance. Review the model’s listing and manual before purchase.
How to Verify a UV System’s Certification
- Find the model number. It's on the product page and on the unit's label.
- Search NSF's database. Go to info.nsf.org/Certified/DWTU. Type the brand in the Manufacturer box and choose NSF/ANSI 55 from the Product Standard menu
- Match the exact model. A similar model number doesn't count. It must be identical.
- Check the class. Class A is intended for treatment of microbiologically contaminated water. Class B is intended for supplemental treatment of drinking water that has already been treated or otherwise determined appropriate for its intended use.
If the packaging names a different certifier, search that organization's listings the same way.
How to Choose the Right Certified UV System
Start with your water source. If you rely on a private well, arrange a water test and identify any treatment needed before selecting UV. For supplemental treatment of drinking water already considered safe, compare Class B models.
Check the water quality limits. Sediment, cloudiness, and other conditions can interfere with UV treatment; follow the exact manufacturer manual.
Size for peak demand. Compare your required flow with the model's certified flow rate, not a different model's standard rating.
Plan maintenance. Follow the certified system's lamp, sleeve, sensor, and service instructions. If you need help matching a model to a water test, contact ESP Water Products.
Questions about certification or choosing a system? Call 1 (877) 377-9876.
NSF Water Treatment Certification Frequently Asked Questions
What is the difference between NSF/ANSI 42 and NSF/ANSI 53?
NSF/ANSI 42 primarily addresses aesthetic water-quality claims such as chlorine taste and odor reduction. NSF/ANSI 53 addresses specific contaminant-reduction claims associated with health effects. Always check the exact certified claims for the individual product.
What does NSF/ANSI 58 mean?
NSF/ANSI 58 applies to reverse osmosis drinking water treatment systems and RO components. Certification may apply to a complete system or to an individual component, such as an RO membrane, so check the exact certification listing.
Does an NSF-certified filter make the entire water treatment system NSF certified?
No. Certification of an individual filter, membrane, pump or other component does not automatically certify the complete assembled water treatment system.
What is NSF/ANSI 401?
NSF/ANSI 401 addresses certified reduction claims for specific emerging compounds or incidental contaminants. The exact claim depends on the product. For example, the Omnipure Q5615 is certified under NSF/ANSI 401 for microplastics reduction.
What does NSF certification mean for a UV system?
A specific model has been assessed by a certification organization against a stated standard and its listed claims. For UV systems, check whether the listing says NSF/ANSI 55 Class A or Class B, and verify the model and rated flow.
What is the difference between Class A and Class B?
Class A is intended for treatment of microbiologically contaminated water and has a minimum UV dose of 40 mJ/cm². Class B is for supplemental treatment of drinking water already considered safe and has a minimum UV dose of 16 mJ/cm². Check the exact listing and operating conditions.
Do I need a certified UV system at home?
Your choice depends on your water source, test results, treatment goal, and any local requirements. For an untreated private well, test the water and compare appropriate Class A models. For supplemental treatment of drinking water already considered safe, compare Class B models.
What does NSF/ANSI 55 cover?
It covers specified performance and other requirements for ultraviolet drinking water treatment systems. Its Class A and Class B listings have different intended uses. It is not a certification that a UV system removes lead, chemicals, or hardness.
Is Class A certification required for my well?
Requirements vary by location and use. A private well owner should test the water and check local requirements. Class A is intended for microbiologically contaminated water, but the right installation can require pretreatment and must meet the model’s water quality and flow limits.
How do I know whether a UV system is certified?
Find the exact model number and the organization named on its mark or product documentation. Search that organization’s official listing and match the standard, class, model, and rated flow.
Does “tested to NSF/ANSI 55” mean certified?
No. Ask which organization certified the exact model, then confirm its standard and class in that organization’s official listing.
Can a Class B UV system treat untreated well water?
Class B is intended for supplemental treatment of water already considered safe. Test untreated well water and evaluate a Class A model and any needed pretreatment.
Does an NSF/ANSI 55 UV system remove lead or chemicals?
NSF/ANSI 55 addresses UV treatment claims. It does not, by itself, certify removal of lead, chemicals, or hardness. Check separate product claims and listings for those concerns.
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