NSF/ANSI 42-2021: Drinking Water Treatment Units, Aesthetic Effects

Picture a glass of water. Odds are it shares a striking similarity with the one above. We like our water a certain way, especially the type we need to drink. Setting aside the variance in appearance, odor, etc., in whatever form it takes to occupy 71% of the earth’s surface and an indeterminate amount of the cosmos—water likely arrived on our planet via comets and asteroids—we want this dipolar transparent liquid to be pleasant. Appearance is important for the substance that we literally drink for survival.

Aesthetics extends beyond water’s appearance. In fact, the systems covered by NSF/ANSI 42-2021: Drinking Water Treatment Units – Aesthetic Effects reduce substances that can affect the aesthetic quality of water (impurities such as chlorine and taste/odor), but they also can add chemicals for scale control or limit microbial growth in the system.

Water Treatment Systems Covered by the NSF/ANSI 42 Standard

The treatment systems addressed by NSF/ANSI 42-2021, which can be either point-of-use (under-the-sink, water pitcher) or point-of-entry (whole house), are designed to reduce specific substances that may be present in public or private drinking water considered to be microbiologically safe and of known quality.

The American National Standard establishes minimum requirements for materials, design and construction, and performance of drinking water systems dealing with aesthetic (nonhealth) effects contaminants in water supplies. This includes gas chromatography/mass spectroscopy (GC/MS) analysis, structural integrity, and test methods for bacteriological performance. It also specifies minimum product literature and labeling information for a manufacturer to supply to authorized representatives and system owners.

Changes to NSF/ANSI 42-2021

NSF/ANSI 42-2021 revises the 2020 edition of the same American National Standard for filters that limit the aesthetic effects of drinking water treatment units. In keeping the document current, this revision:

  • Clarifies the requirements for drinking fountains under the general performance requirements of the standard.
  • Updated the minimum air gap requirement for drinking fountain outlets from 2 inches to 1 inch to be aligned with other industry standards and codes.
  • Added a minimum TOC (total organic carbon) requirement (> 1.0 mg/L) to the chloramine test water in Section, Influent challenge.”
  • Added Normative Annex 6, “Preparation of TOC solution using tannic acid.”
  • Specified that tannic acid be used per Annex N-6 to achieve a consistent level of TOC in the starting test water when it can’t be achieved from the natural water.
  • Added Section, “Allowance for chlorine and/or monochloramine claims.”
  • Clarified the chlorine reduction claim requirements in Section 7.3, “Chemical reduction testing.”
  • Added clarifying language for chloramine sampling under Section
  • Changed the chloramine reduction test in from a maximum effluent concentration (0.5 mg/L)
  • to a percent reduction (≥ 80%).
  • Updated the minimum 2-L sample requirement to a recommendation in Section 4.2.3.
  • Updated the fine media extraction test method in Section

NSF/ANSI 42-2021: Drinking Water Treatment Units – Aesthetic Effects is available on the ANSI Webstore.

Changes to NSF/ANSI 42-2020

The previous edition of this American National Standard also underwent some significant revisions that might be useful for its users to know. The 2020 edition of NSF/ANSI 42 featured clarifications on:

  • The method for powdered activated carbon and polymer binders.
  • The test pressure for non-pressurized water treatment devices.
  • How systems shall be tested with and without adsorptive or absorptive for replacement elements.

The new revision also added:

  • An exemption 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.
  • Guidance on extraction testing for hot and cold water dispensers.

Furthermore, NSF/ANSI 42-2020 corrected the improper use of requirements in notes and information annexes.

Changes to NSF/ANSI 2019

Even further back in this standard’s history, NSF/ANSI 42-2019, when compared to the 2018 version, clarified testing for pH in the sampling procedures for chloramine reduction testing, and it corrected a previous error in Table 5.1 for “Structural integrity testing requirements.”

All Annexes in NSF/ANSI 42-2019 were changed from alpha characters to numeric, preceded by “Normative” or “Informative.” For example, the previous Annex A became Informative Annex 1 (I-1).

Drinking Water Treatment Units – Health Effects

For guidance on drinking water treatment units that reduce health-related contaminants, please refer to NSF/ANSI 53-2020: Drinking Water Treatment Units – Health Effects.

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