What Do NSF/ANSI 401, 53 and 58 Actually Mean?

Water filter certifications can be confusing, especially when filters are labeled with numbers like NSF/ANSI 53, 58, or 401.

NSF/ANSI numbers represent rigorous performance standards set by NSF International and the American National Standards Institute (ANSI), two leading bodies responsible for certifying the safety and effectiveness of water treatment products.

This article explains what each of these standards means, how they differ, what they cover, and how you can use this knowledge to make smarter choices.

What Is NSF Certification?

NSF International is a global, independent public health and safety organization that develops testing protocols and certification programs for a wide range of consumer products, including drinking water treatment units. The ANSI (American National Standards Institute) designation confirms that NSF’s standards have been developed in accordance with U.S. consensus based processes.

A product labeled “NSF/ANSI certified” has passed rigorous tests to verify that it reduces specific contaminants to below established safety thresholds under real-world conditions, including flow rate, temperature, and capacity constraints. Certification includes both performance testing and annual inspections of manufacturing facilities to ensure consistency over time.

NSF/ANSI 53 – Filters for Health Risks

NSF/ANSI Standard 53 is among the most commonly cited certifications and is specifically focused on filters that reduce contaminants with established health effects. These include:

• Heavy metals: Lead, mercury, cadmium
• Organic chemicals: Benzene, MTBE, pesticides like atrazine
• Microorganisms: Cysts such as Giardia and Cryptosporidium
• Volatile Organic Compounds (VOCs)
• Asbestos

To meet NSF 53 requirements, a filter must reduce the contaminant to a level below the Maximum Contaminant Level (MCL) defined by the EPA or WHO. Filters are tested for consistent performance over their full rated lifespan.

NSF/ANSI 58 – Certification for Reverse Osmosis Systems

NSF/ANSI Standard 58 applies exclusively to reverse osmosis (RO) systems, which use a membrane to remove a broad spectrum of contaminants. RO systems are tested for:

• Arsenic (III and V)
• Nitrate and nitrite
• Fluoride
• Chromium
• Lead
• Cadmium
• Total Dissolved Solids (TDS)

In addition to contaminant removal, NSF 58 includes structural integrity testing (to ensure tanks and housings don’t fail under pressure), recovery ratio benchmarks (to measure water efficiency), and safety of materials in contact with drinking water.

Certified RO systems typically remove 90-99% of the contaminants listed above.

NSF/ANSI 401 – Emerging Contaminants

NSF/ANSI Standard 401 is a newer certification developed in response to growing concern over “emerging contaminants”, which are substances increasingly found in drinking water but not yet regulated by the EPA.

These include:

• Pharmaceuticals (e.g., ibuprofen, atenolol, carbamazepine)
• Hormones (e.g., estrone)
• Industrial chemicals (e.g., BPA, PFOA, PFOS)
• Herbicides (e.g., linuron)
• Personal care products (e.g., DEET, triclosan)

To gain 401 certification, filters must reduce at least 15 of these contaminants under standardized conditions. While these substances are not legally regulated, they are frequently detected in municipal water supplies at low levels and may pose long-term health risks.

This standard does not guarantee complete removal, but certified products must demonstrate meaningful reduction.

Summary of Key Differences

Standard	Scope	Examples of Contaminants	Applies To
NSF/ANSI 53	Health-based contaminants	Lead, mercury, asbestos, pesticides, cysts	Carbon-based filters
NSF/ANSI 58	Reverse osmosis systems	Fluoride, arsenic, nitrate, chromium, TDS	RO systems
NSF/ANSI 401	Emerging, unregulated contaminants	BPA, pharmaceuticals, hormones, PFAS	Select advanced filters

How These Differ from NSF/ANSI 42

NSF/ANSI 42 is often confused with the above standards, but it only addresses aesthetic improvements such as the reduction of chlorine taste, odor, and visible particulates. It does not certify health-related contaminant removal.

Many filters that claim “NSF Certified” only meet Standard 42, which is not enough to protect against harmful contaminants like lead or pesticides.

Common Misconceptions and Marketing Traps

A product may only be certified for one contaminant (e.g., chlorine under NSF 42), but advertise NSF certification broadly.

Just because a filter is certified under NSF 53 doesn’t mean it removes all heavy metals or VOCs. You must check the specific list on the product’s data sheet.

Pitcher filters are limited: While convenient, most pitcher filters are only certified for aesthetic improvements or a few contaminants like chlorine or lead.

ROs typically need pre- and post-filtration, and maintenance is critical to performance. Not all RO systems are certified for every target contaminant under NSF 58.

How to Check a Product’s Certification

1. Visit NSF’s Product Listings
2. Enter the brand or model number
3. Check the certification standard (e.g., 53, 58, 401)
4. Review the list of certified contaminants

This is the most accurate way to determine whether a filter does what it claims.

When Filters Are Certified by Other Agencies (Not NSF)

Not all water filters are certified directly by NSF International. In fact, many reputable manufacturers use independent third-party laboratories that test to the same NSF/ANSI standards but are accredited by other certification bodies.

These alternative agencies may include:

• IAPMO R&T (International Association of Plumbing & Mechanical Officials – Research & Testing)
• WQA (Water Quality Association)
• CSA Group (Canadian Standards Association)
• UL (Underwriters Laboratories)
• UL Water Quality (formerly WQA Gold Seal Program)
• TÜV SÜD (based in Europe, recognized for international testing)
• Intertek (ETL certification)

These organizations follow the same ANSI-approved testing methodologies and are themselves accredited by national or international bodies, such as the American National Standards Institute (ANSI), the Standards Council of Canada (SCC), or the International Accreditation Service (IAS).

Why This Matters

Some consumers assume NSF is the only “valid” certification source, but this isn’t true. As long as the certifying agency is ANSI-accredited and lists NSF/ANSI standards, the certification is considered equally credible.

However, be wary of vague phrases like “tested to NSF standards” or “meets NSF guidelines” without a certifying agency or documented proof. Genuine certifications always list the standard, the agency, and often the specific contaminants addressed.

Examples of Popular Filters and Their Certifications

Brand/Model	NSF 42	NSF 53	NSF 58	NSF 401	Notes
Brita Standard	✔	✘	✘	✘	Taste and odor only
Brita Longlast+	✔	✔	✘	✘	Certified for lead
Epic Nano*	✔	✔	✘	✔	Third-party tested by EPA accredited labs.
Aquasana Claryum	✔	✔	✘	✔	Certified for PFOA, BPA, pharmaceuticals
APEC RO-90	✘	✘	✔	✘	RO system with TDS, fluoride, arsenic reduction
Clearly Filtered Pitcher*	✔	✔	✘	✔	Third-party lab tested.

*Note: “Epic Nano” and “Clearly Filtered” have published test results for many contaminants, but are not officially NSF/ANSI 401 certified.

• Epic states testing is done by EPA accredited laboratories and have been individually tested at levels exceeding NSF/ANSI standards 42, 53, & 401.
• Clearly Filtered states their products are independently tested by third-party labs to comply with NSF/ANSI standards 42, 53, 401 and 473.

Why This Matters for Your Water

The reality is that no single filter removes everything. Understanding NSF/ANSI certifications lets you match the right filter to your specific water quality concerns:

• Concerned about lead or cysts? Look for NSF 53.
• Need to remove fluoride or arsenic? Choose NSF 58-certified RO systems.
• Want protection from modern trace chemicals like PFOA or ibuprofen? Look for NSF 401.

And always verify those claims through third-party documentation, not just packaging.

NSF/ANSI Standards 53, 58, and 401 are not just marketing labels. They’re detailed, lab-verified certifications that ensure a water filter does what it claims. Knowing what each one covers, and how to confirm certification, is key to making a confident, informed decision about your drinking water.