Water and Wastewater Protective Coating Systems
Article 05 of 24
Potable-Water Coatings, NSF/ANSI/CAN 61, and Product Certification
A coating used in drinking-water contact must satisfy the project’s performance requirements and any applicable health-effects certification requirements. One does not replace the other.
Potable-Water Service Requires a Higher Level of Verification
A coating applied inside a drinking-water tank becomes part of the water-contact system. The owner and public depend on the installed lining to protect the structure without introducing unacceptable levels of contaminants into the water.
The contractor must therefore verify more than adhesion, corrosion resistance, and expected service life. The selected product may also need current third-party certification for drinking-water contact under the conditions in which it will be used.
Product selection should never be based solely on a label, brochure statement, old approval letter, or verbal assurance that a material is “safe for potable water.”
What NSF/ANSI/CAN 61 Addresses
NSF/ANSI/CAN 61 is a consensus standard addressing the health effects of materials, components, products, and systems that contact drinking water. It evaluates substances that may be extracted or leached from a product into the water under defined test conditions.
Protective coatings and linings are among the products that may be evaluated and certified under the standard. Certification provides evidence that the listed product met the applicable health-effects requirements when tested and used within the limitations of its listing.
The certification belongs to the specifically listed product, manufacturer, formulation, and use conditions. It should not be extended to a different product merely because the chemistry, product name, or manufacturer appears similar.
What NSF/ANSI/CAN 61 Does Not Establish
NSF/ANSI/CAN 61 certification should not be interpreted as proof that a coating is suitable for every drinking-water structure or that it will provide adequate physical performance.
The standard does not, by itself, establish:
- Adhesion to the project substrate
- Corrosion resistance or expected service life
- Surface-preparation requirements
- Resistance to abrasion, impact, cracking, or movement
- Suitability for the specific water chemistry or temperature
- Compatibility with an existing coating
- Suitability for exterior weathering
- A complete quality-control or inspection program
- Compliance with every project, owner, state, provincial, or local requirement
Health-effects certification and coating-performance qualification are separate requirements. A successful project must satisfy both.
Certified Product Does Not Mean Unlimited Use
A certified listing may contain important use limitations. The contractor, manufacturer, engineer, and owner should verify that the proposed application falls within those conditions.
Listing conditions may address:
- Minimum tank or vessel size
- Minimum pipe diameter
- Maximum surface-area-to-water-volume ratio
- Water-contact temperature
- Number of coats
- Maximum or specified film thickness
- Required cure time
- Required cure temperature
- Product color or formulation
- Primer or complete system requirements
- Special flushing, conditioning, or preparation instructions
A product may be certified for a large tank but not for a small vessel because the ratio of coated surface area to water volume is different. A product certified for cold-water contact may not be listed for elevated-temperature service.
Verify the Current Official Listing
Certifications can be added, revised, suspended, or withdrawn. A printed document retained from an earlier project may no longer reflect the current listing.
Before submitting or purchasing the product:
- Search the certification organization’s current official product database.
- Confirm the manufacturer’s exact legal name.
- Confirm the exact product name and formulation.
- Read every use limitation and note associated with the listing.
- Compare the listing with the project’s tank size, pipe diameter, temperature, thickness, number of coats, and cure conditions.
- Save a dated copy or record of the verified listing for the submittal and project file.
- Request written clarification if the proposed use does not clearly fall within the listing.
Do Not Substitute Other Claims for Certification
Marketing language can be misunderstood. Statements such as “food grade,” “non-toxic when cured,” “complies with FDA requirements,” “meets drinking-water requirements,” or “previously approved for potable water” do not necessarily establish current NSF/ANSI/CAN 61 certification.
Likewise, a safety data sheet does not establish potable-water approval. An SDS communicates workplace hazard information; it is not a drinking-water certification.
Use the specific certification and documentation required by the project. When terminology is unclear, request written confirmation from the engineer, owner, manufacturer, and certification organization as appropriate.
Certification Applies to the Installed System
The certification review begins with the product listing, but compliance must be preserved during installation.
The contractor must control:
- Product identity and batch traceability
- Storage temperature and shelf life
- Correct component ratio
- Mixing and induction requirements
- Use of only permitted thinners or additives
- Required primer and complete coating system
- Wet- and dry-film thickness
- Recoat intervals
- Environmental conditions during application and cure
- Minimum cure time before disinfection or filling
- Approved repair materials and procedures
Using an unapproved thinner, exceeding a listed thickness, shortening the cure, or combining components from unrelated systems may move the installation outside the conditions that were evaluated.
Potable-Water Coating Performance Still Matters
After confirming certification, determine whether the complete coating system is technically suitable for the structure and exposure.
Evaluate:
- Concrete, steel, ductile iron, or other substrate
- New construction versus rehabilitation
- Existing coating condition and compatibility
- Water chemistry, disinfectants, and treatment chemicals
- Immersion temperature
- Expected movement, cracking, and vibration
- Abrasion and cleaning methods
- Surface-preparation requirements
- Application access and equipment
- Available environmental control
- Shutdown and cure schedule
- Inspection, testing, repair, and future maintenance
AWWA D102 and Steel Water-Storage Tanks
AWWA D102 provides requirements for coating steel water-storage tanks, including materials, coating systems, surface preparation, application, inspection, and testing. The project specification may invoke a particular edition and modify or supplement its requirements.
The contractor should identify:
- The specified interior and exterior coating systems
- Surface-preparation standards
- Stripe-coat requirements
- Required colors and number of coats
- Wet- and dry-film thickness requirements
- Environmental limitations
- Inspection and testing requirements
- Interior cure, cleaning, and disinfection requirements
- Documentation and final acceptance requirements
NSF/ANSI/CAN 61 certification and AWWA D102 address different aspects of the project. One should not be used as a substitute for the other.
Cure Before Disinfection and Filling
A coating can appear dry while remaining insufficiently cured for immersion. Filling the structure too early can affect coating performance, water quality, taste, odor, adhesion, and future service life.
Cure depends on more than elapsed time. Temperature, ventilation, humidity, film thickness, mixing accuracy, solvent release, air movement, and substrate conditions can affect the cure rate.
Follow the specification and current manufacturer instructions for ventilation, cure time, cure verification, disinfection, flushing, water-quality testing, and return to service. Do not shorten the cure simply because the owner needs the tank back in service.
Repairs Require Approved Materials
A holiday, pinhole, damaged area, or thin spot should not be repaired with an unlisted or unrelated material simply because it is convenient.
Use the repair material and procedure approved for the coating system and potable-water service. Document the repair location, preparation, material, batch number, application, cure, retesting, and acceptance.
Potable-Water Submittal Checklist
- Identify the structure, substrate, coating-system number, and intended water-contact service.
- Provide current technical and safety data sheets.
- Provide the current NSF/ANSI/CAN 61 listing when required.
- Highlight all listing restrictions applicable to the project.
- Show the primer, repair material, resurfacer, intermediate coat, lining, and repair materials.
- Identify the required thickness of each coat and the total system.
- Provide surface-preparation and environmental requirements.
- Provide mixing, application, recoat, and cure instructions.
- Provide inspection, holiday-testing, and repair procedures.
- Provide cleaning, disinfection, flushing, and return-to-service instructions.
- Identify manufacturer technical-service and warranty requirements.
- Clearly identify every proposed deviation from the specification.
Article 05 Knowledge Check
- What does NSF/ANSI/CAN 61 evaluate?
- Why does certification not prove that a coating will perform successfully on a particular structure?
- What types of use limitations may appear in a certified-product listing?
- Why should the current official listing be checked instead of relying on an old certificate?
- Why is an SDS not evidence of potable-water certification?
- How can installation practices move a coating outside its evaluated conditions?
- Why must the lining reach the required cure before disinfection and filling?
Technical References and Further Study
- NSF International: NSF/ANSI/CAN 61, Drinking Water System Components - Health Effects.
- NSF International: Official certified drinking-water system component listings. Verify the current product listing and all limitations.
- American Water Works Association: AWWA D102, Coating Steel Water-Storage Tanks. Use the edition required by the project.
- American Water Works Association: Applicable standards for steel tanks, bolted tanks, water pipe, protective coatings, disinfection, and water-system construction.
- Coating manufacturer: Current product data, certification documentation, application instructions, repair procedures, cure requirements, and potable-water service limitations.
- Project documents: Coating schedule, specifications, approved submittals, owner standards, and written clarifications.
Certifications, listings, standards, and product instructions change. Always verify the current requirements before submitting, purchasing, applying, repairing, disinfecting, or placing the system into service.
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