NSF/ANSI 53-2025: Drinking Water Treatment Units, Health Effects

Water is important. It makes up 60% of your body and 71% of your planet’s surface. In fact, in the over-dozen times we’ve focused on drinking water standards on this blog, their purpose has been clear: drinking water needs to be safe for consumption to support public health. Aiding the performance of treatment units that minimize the health effects of drinking water, NSF/ANSI 53-2025, Drinking Water Treatment Units – Health Effects outlines various requirements.

American National Standard for Drinking Water Treatment Units

Units that reduce health-related contaminants in drinking water are one of the final bulwarks that protect the public from harm.

Specifically, NSF/ANSI 53-2025 establishes minimum requirements for materials, design and construction, and performance of drinking water treatment systems designed to reduce specific health-related contaminants in public or private water supplies. These systems, point-of-use (POU) and point-of-entry (POE), reduce substances considered established or potential health hazards, whether chemical or particulate in nature. This includes radon, asbestos, Cryptosporidium oocysts, and inorganic volatile chemicals, among numerous other contaminants listed in tables in the standard.

NSF/ANSI 53-2025 applies to systems can be used to treat all or part of the portable water at the inlet to a residential facility or a bottled water production facility, and the standard includes the materials and components of these systems.

The standard also includes product literature and labeling information.

Changes to NSF/ANSI 53-2025

Compared to the previous edition of the same American National Standard from 2024, NSF/ANSI 53-2025 has undergone the following changes of note:

The cation components of the PFAS reduction test water were updated in Section 7.2.6.5, “Cycle Time,” and Table 7.9, “PFAS influent water characteristics,” to prevent scaling/premature filter plugging.
Optional nitrate influent levels were added to Table 7.2, Chemical reduction requirements,” and Table 8.1, “Performance data sheet reduction claims,” to allow testing to one of three average influent challenge concentrations: 30 ± 10, 70 ± 10, or 110 ± 10 mg/L.
New Informative Annex 10 (I-10), “Nitrate/nitrite drinking water treatment standards,” was added.
The influent and effluent levels for hexavalent chromium were lowered from 0.3 mg/L to 0.1 mg/L to meet the California MCL in Table 7.14, “General metals reduction requirements,” and Table 8.1.
Effluent limits were updated for PFOA and PFOS to align with US EPA MCLs. This included the following changes:
New Sections 7.2.1.1.1, “PFAS reduction claims,” and 7.2.1.1.1.1, “Total PFAS demonstrative examples,” were added.
Language was added to Section 7.2.6, “Non-regenerating PFAS reduction testing.”
PFAS was removed from Tables 7.1, “Chemical reduction requirements,” and 8.1.
Section 7.2.6.1 and former Table 7.7 were removed.
Language was modified regarding PFAS in Table 7.9, “PFAS influent water characteristics.”
New Table 7.2, “Chemical reduction requirements for PFAS,” was added.
New Table 8.2, “Performance data sheet reduction claims for PFAS compounds,” was added.
Cycle time and sampling for lead reduction testing were harmonized in Sections 7.4.3.6, “Cycle time,” and 7.4.3.8, “Sampling,” with language previously approved for other applicable sections.
Text was revised in Section 4.2.3, “Exposure,” to indicate that for material evaluation, pour through products do not need to be flushed after the 24-h exposure and water collection.
Maximum RLs were removed from DWTU extraction testing parameter tables [Table 4.1, “Extraction testing parameters (metals), Table 4.2, “Extraction testing parameters (semivolatiles), Table 4.3, “Extraction testing parameters (volatiles)”]
A new requirement was added to Section 4.2.1.3 to seek the lowest detection limits via both sample exposure and analysis.
Instructions were clarified in Sections 4.2.3.3, 7.2.4.1.2, “Calculation of progeny activity at end of life,” and former 7.2.6.5 (now 7.2.6.4, “PFAS reduction test water”).

The standard document also contains an errata correcting the previously published version of NSF/ANSI 53-2025.

NSF/ANSI 53-2025, Drinking Water Treatment Units – Health Effects is available on the ANSI Webstore and in the following Standards Packages: NSF Drinking Water Treatment Units Complete Set and NSF Drinking Water Treatment Units Set.

Drinking Water Treatment Units Aesthetic Effects

For guidance on drinking water treatment units the reduce the presence of aesthetic contaminants, please refer to our post NSF/ANSI 42-2025: Drinking Water Treatment Units, Aesthetic Effects.

Past Revisions of NSF/ANSI 53

Due to the sheer importance of drinking water, this American National Standard developed by NSF International is published annually. If you need any past editions of ANSI 53, you can find them as historical standards on the ANSI Webstore. You can also read about the many changes made to past revisions below:

Changes to NSF/ANSI 53-2024

NSF/ANSI 53-2023 revised the 2023 edition and went through the following changes of note:

The use of Cryptosporidium parvum stock was allowed in Sections 7.3.2.1, “Live C. parvum oocyst reduction,” and N-1.1, “Summary of method,” (in Normative Annex 1, “Test method for detecting and enumerating C. parvum oocysts”) after 8 weeks with validation by the vendor or lab.
The influent challenge for asbestos was changed to solely chrysotile fibers in Section 7.3.1.4.3, “Influent challenge – Asbestos.”
Annexes N-1 and N-2, “Test method for detecting and enumerating polystyrene microspheres,” were clarified regarding MDL, QC, equipment requirements, matrix spike recovery and controls limits, negative control definition, microscopy analysis and interpretation, and analyst verification for C. parvum and polystyrene microspheres.
Section 7.2.4.1.2 calculations were updated for radon progeny activity at end of life to replace the use of the EPA Carb Dose program, which is no longer available.
New Informative Annex 9, “Key elements for remote monitoring of POE and POU DWTS designed for lead removal,” was added.

Changes to NSF/ANSI 53-2023

Compared to the 2022 revision, NSF/ANSI 53-2023 has undergone the following changes of note:

The current operational cycles and sampling specified throughout Sections 7.2, “Chemical reduction claims,” and 7.4, “Metals reduction testing,” were harmonized with language previously approved for NSF/ANSI 42 and 401.
Updates were made to Sections 8.1.1 and 8.4.1 to allow installation, operation, maintenance instruction manuals, and performance data sheets to be publicly accessible online, as long as hard copies are provided upon request.
Values were updated in Tables 4.3, “Extraction testing parameters (semivolatiles),” 7.1, “Chemical reduction requirements,” 7.6, “Organic chemicals included by surrogate testing,” and 8.1, “Performance data sheet reduction claims,” for maximum reporting limits and maximum effluent concentrations for ethylbenzene, toluene, and xylenes.
Test protocols were added throughout Section 7, “Elective performance claims – Test methods,” for pour through and batch treatment systems with influent reservoirs that hold more volume than the effluent reservoir, or that require multiple drain events to treat a single influent reservoir volume.
Language was added in Section N-5.2, “Mechanical filtration of waters,” to allow the use of a mechanical filter prior to the test unit that does not impact the chemistry requirements of the standard.
Water temperatures were standardized for hydrostatic structural integrity testing and chemical reduction testing, including POE, under General test water in Sections 5.4.2, 6.1.4.2, and throughout Sections 7.2, 7.3, 7.4, and 7.5.
New Sections 7.2.1.5.3 and 7.2.1.5.4 for adjusting pH and TDS for organic chemical reduction testing.
Treatment train options were clarified in Section N-6.1, “Requirements for the evaluation of a system containing multiple, sequential treatment technologies.”

Changes to NSF/ANSI 53-2022

More PFAS compounds were added to the chemical reduction claims.
Test requirements were clarified for point-of-use (POU) versus point-of-entry (POE) devices, including adding two methods of testing POE systems: using one full size POE unit or two properly sized scaled down units.
U.S. EPA Method 521 to the U.S. EPA Method(s) column of Table 4.2, “Extraction testing parameters (semivolatiles).”
The word “system” was changed to “component” in Section 8.3.2 for information to be stated on replacement components, ensuring consistency with language in NSF/ANSI 42.
U.S. EPA Methods 505, 508, and 525 were added to several substances in Table 7.1, “Chemical reduction requirements,” as an option for lab testing.

Changes to NSF/ANSI 53-2021

The minimum air gap requirement for drinking fountain outlets was revised from 2 inches to 1 inch.
Specification was added noting that tannic acid can be used per Annex N-7, “Preparation of TOC solution using tannic acid,” to achieve a consistent level of total organic carbon (TOC) in the starting test water when it can not be achieved from the natural water.
1,2,3-trichloropropane was added to the chemical reduction claims.
Language was corrected to indicate that batch systems sampling is to be taken when the filling time is increased by 33%, 100%, and 300%.
The acceptance criteria for the microsphere test was clarified to pertain to every effluent sample point in Sections 7.3.2.2.1, “Polystyrene microsphere reduction claim for systems other than those used in bottled water plants,” and 7.3.2.3.1, “Polystyrene microsphere reduction claim.”
Section N-1.6.1, which covers sample collection for Cryptosporidium parvum oocysts, was corrected with regard to the polyoxyethelene sorbitan mono-oleate concentration and removed the requirement to collect influent samples in triplicate.
The minimum 2-L sample requirement was updated to a requirement.
Corrections were made to terminology.
References were updated.
An analyte was added to Table 4.2, “Extraction testing parameters (semivolatiles),” and Table 8.1, “Performance data sheet reduction claims.”
Evaluation criteria for n-nitrosamine removal were added as new Section 7.2.7, “N‐nitrosodimethylamine (NDMA) reduction testing,” and new Informative Annex 7, “Explanation of scope and purpose of N-nitrosodimethylamine (NDMA) reduction claim.”
Two instances of Pb(NO3) were corrected to Pb(NO3)₂ in Section 7.4.3.5.2.3.1, which covers the preparation of the solutions for generating the lead pH 8.5 test water.
A column was added for the individual influent sample point limit to Table 7.13, “Mercury reduction requirements.”

Changes to NSF/ANSI 53-2020:

A new statement was added for conditioning and conditioning volumes for microcystin reduction claims.
The test pressure for nonpressurized water treatment devices was clarified.
Guidance on extraction testing for hot and cold water dispensers was added.
An exemption was added for cyclic pressure testing for components downstream of the system on/off valve that are not subject to pressure under the off mode and either contain no media subject to pugging or are not designed to contain media.
Clarification was provided on how systems shall be tested with and without adsorptive or absorptive for replacement elements.

Changes to NSF/ANSI 53-2019:

A performance reduction claim was added for perfluorocctanoic acid (PFOA) and perfluoroctane sulfonate (PFOS) for nonregenerable drinking water treatment devices that use anion exchange media. This is found in new section 7.2.6, “Nonregenerating PFOA/PFOS reduction testing.”
The pass/fail criteria for lead reduction (Tables 7.10 and 8.1) was changed from 10 μg/L to 5 μg/L. This alteration reflects proposals at the state, federal, and international levels.
A previous error in Table 5.1, “Structural integrity testing requirements,” was corrected, adding a heading for “Complete systems” and “Components.”
Keeping in line with editorial changes to made to many NSF standards published in 2019, the annexes were changed from alpha characters to numeric and are now preceded by “Normative” or “Informative.” For example, “Annex A” from NSF/ANSI 53-2018 is called “Normative Annex 1 (N-1)” in NSF/ANSI 53-2019.

Changes to NSF/ANSI 53-2018:

An asbestos reduction protocol was added for batch treatment systems in Section 7.3.1, “Asbestos reduction claims.”
The standard clarified language on systems that include components or functions covered under other NSF standards.
This revision clarified “product literature requirements” under Section 8.3, “Replacement components.”
For drinking water treatment devices that use activated carbon absorption, this edition of the standard added a performance reduction claim for perfluorocctanoic acid (PFOA) and perfluoroctane sulfonate (PFOS).

Changes to NSF/ANSI 53-2017:

Sample collection for systems containing multiple potable water outlets under 4.2.3, “Exposure” were addressed.
Evaluation criteria columns from Tables 4.1 – “Extraction testing parameters (metals),” 4.2 – “Extraction testing parameters (semi-volatiles),” and 4.3 – “Extraction testing parameters (volatiles)” were removed and instead referenced the evaluation criteria in Annex D Table D.1 in NSF/ANSI 61.
Performance guidelines for drinking water treatment systems designed to reduce microcystins in public water supplies were added.
New normative Annex J, “Preparation of TOC solution using tannic acid.”
New informative Annex K, “Explanation of scope and purpose of microcystins reduction claim.”

Changes to NSF/ANSI 53-2016:

Language was added to state that systems be conditioned using the test water with the specified contaminant for chemical reduction claims.
CAS numbers were added to Table 4.1 (previously Table 1) of the materials evaluation criteria.
Sampling point instructions for squeeze bottles in Annex E were clarified.
Tables were changed to reflect the appropriate section in which each is located.

Questions About NSF/ANSI 53?

NSF/ANSI 53 is developed by NSF International.

Please direct any technical questions relating to this American National Standard to the developer. You can find the contact information for all ANSI-accredited standards developers here: List of ANSI-Accredited Standards Developers (ASDs).

For further information, please refer to: Who to Contact for Standards Related Questions.