Getting Ahead of the Latest Potable Water Standard


By Sherwin-Williams Protective & Marine

The new standard will eliminate a number of lining systems from use that are currently rated for potable water service, forcing asset owners, engineers and applicators to rethink specifications. Photo: Courtesy of dixon engineering inc.

A formidable force in the potable water industry is lurking in the depths, ready to strike at a number of existing lining technologies and take them off the market. It remains to be seen what products will stay in the water storage tank after that deadly strike. But, with certainty, there will be fewer linings in the pool of available technologies.

The big fish poised to devour several proven lining systems from spec sheets is the new NSF/ANSI/CAN 600: Health Effects Evaluation and Criteria in Drinking Water standard. Taking effect in January 2023, the standard proposes a drastic reduction of the Maximum Contaminant Levels (MCLs) of xylene, toluene and ethylbenzene found within coating and lining products certified for potable water storage use. As such, a broad number of solvent-based coatings — mainly thin-film epoxies — will likely no longer be approved for use.

The fate of those technologies will be sealed by the time NSF/ANSI/CAN 600 goes into full effect, and much uncertainty abounds related to which systems will be approved. However, the industry can be certain that the majority of permitted products will be formulations featuring 100% volume solids or technologies that use exempt solvents for volatile organic compound (VOC) compliance that are not identified in the current regulation changes. Such ultrahigh solids materials include minimal to no solvents and can therefore easily meet NSF/ANSI/CAN 600 guidelines. In addition, certain high-solids coatings that lack the restricted solvents will be permitted.

With a limited number of materials currently approved in advance of the finalized NSF/ANSI/CAN 600 guidelines, asset owners, engineers and applicators may want to begin specifying those materials today to get ahead of the looming deadline. Doing so will help them avoid the potential situation of the specified lining for a water storage tank built in late 2022 not being approved when the tank is coated in 2023, for example. Making an early switch may be especially advantageous for applicators, as many may desire to learn how to spray the ultrahigh solids formulations using plural-component equipment, compared to the single-leg equipment they’ve been using to apply thin-film epoxy linings.

The Rush to 100% Solids Epoxies

By reducing MCLs for xylene, toluene and ethylbenzene in lining materials, the NSF/ANSI/CAN 600 standard seeks to improve drinking water quality. Such solvents may leave a hint of chemical taste or odor in potable water — especially immediately following a lining application — making them a common reason for water samples failing taste tests prior to returning newly relined tanks to service. Switching to NSF/ANSI/CAN 600-approved 100% solids technologies for coatings applied inside potable water storage tanks, transmission lines and water treatment assets should all but eliminate those failures.


Passing the Taste Test Challenge — The First Time

After relining potable water storage tanks, municipal water managers typically must await results from a discerning panel of taste testers. A “pass” means a quick return to service. A “fail” means draining thousands of gallons of water, refilling the tank and trying again — with budget dollars essentially going down the drain.

Having failed on the first try for nearly every water tank it had relined in recent years, Saint Paul Regional Water Services (SPRWS) no longer wanted to leave this final step between immediate or delayed water service to chance. So when the St. Paul, Minnesota-based utility provider relined its 500,000-gallon Sterling Ave. water tower, it selected Dura-Plate 6000. The 100% solids glass-flake reinforced epoxy lining system from Sherwin-Williams Protective & Marine meets the new NSF/ANSI/CAN 600 standard. SPRWS hoped this qualification would prevent a costly drain and refill scenario.

Thankfully, the utility’s water panel approved the first samples, enabling immediate approval for service. That’s half a million gallons of water that could be used instead of being drained away. Occurring just 30 days after the restoration commenced, the return to service was also accelerated by fast curing times for both the lining system and the tower’s exterior coatings. Given this success, using an NSF/ANSI/CAN 600-approved lining system should help every tank pass the first taste test, saving municipalities time and money.

The restored SPRWS Sterling Ave. water tower passed a discriminating water panel taste test on the first try. PHOTO: COURTESY OF THE SHERWIN-WILLIAMS COMPANY

Beyond their notable solvent reductions, 100% solids linings can enable higher-film builds, fewer coats, reduced labor, better edge retention, better corrosion protection, faster returns to service and overall better lifecycle expectations compared to solvent-borne linings. Therefore, NSF/ANSI/CAN 600 has the potential to reduce costs, enhance long-term durability and streamline project schedules.

As an example, applicators are able to spray 100% solids linings at film builds exceeding 10 mils dry film thickness (DFT) in a single pass. That single coat — plus the common step of applying a stripe coat to welds, corners and edges beforehand — is often sufficient to deliver a minimum 25-year expected service life. Solvent-borne linings typically require at least two coats to build enough coating thickness to meet that service mark. Requiring one less coating pass reduces the project’s labor — its most significant expense — by that same amount, providing noteworthy savings.

Another trait of many 100% solids linings is their enhanced edge retention compared to solvented coatings. With 100% solids linings, far less material dissipates at sharp edges as the coatings cure, leaving thicker film builds on these areas, which can otherwise be especially prone to premature corrosion. That means coated supports, ladders and structures inside the headspace of water tanks — an area rife with corrosive threats from moisture, oxygen and chlorides — will better retain their applied coatings for longer lining lifecycles.

In addition, 100% solids coatings offer efficiency benefits. Unlike solvent-borne linings that may require seven-day cures — or longer — before returning assets to service, many 100% solids applications can be returned to service after 24 hours. Future lining inspections are also easier, as the coatings have a slicker surface than solvented linings, minimizing staining and enabling easier cleaning.

One potential drawback in shifting to 100% solids linings is the learning curve and investment applicators face in spraying the materials. Most applicators use single-leg equipment to spray linings for potable water assets, but 100% solids linings require the use of advanced plural-component equipment. Applicators must be trained on how to properly set the complex equipment to ensure proper mixing of Parts A and B of the coating material. The equipment is also expensive, requiring a significant capital investment to participate in the evolving potable water lining market. Applicators that invest early in equipment and training will be poised to meet the forthcoming market needs.

Olly Olly Oxsol-Free!
High-Solids Lining Cleared for Use

It may come as a surprise that many of today’s solvent-free coatings and linings still contain amounts of select solvents. Those solvents have been granted exempt status based on a number of qualifying factors. Oxsol is a prime example that’s currently permitted in a number of coating formulations for potable water use. However, oxsol’s fate of being identified as a hazardous substance of concern is uncertain. If it retains its exempt status, numerous existing products will still be permitted for potable water use under the new standard. But if oxsol loses that exemption, only a few products may remain on the approved list.

Given the possibility of oxsol losing its exempt status under other proposed regulatory compliance reviews, it may be wise for specifiers and applicators to consider going oxsol-free today. Doing so will put them ahead of the game — if oxsol goes away — while also demonstrating a commitment to further limiting contact between drinking water and solvent-based products.

A new solution for consideration is Sherplate 600 from Sherwin-Williams Protective & Marine. The high-solids lining does not contain xylene, toluene, ethylbenzene or oxsol, ensuring it will be free and clear of NSF/ANSI/CAN 600 guidelines regardless of oxsol’s fate. With about 89% volume solids, the lining is easier to apply than 100% solids formulations and sprays more like traditional solvent-based, single-leg epoxy linings poised for elimination under NSF/ANSI/CAN 600. Therefore, applicators not familiar with plural-component equipment will have an easier learning curve for spraying this product compared to applying 100% solids linings.

With high film-build and high edge-retention capabilities, the Sherplate 600 epoxy lining can also be used for stripe coating welds, edges and corners before completing full lining applications. Certain epoxy formulations containing solvents have been preferred for stripe coating, but those materials are likely on the chopping block under NSF/ANSI/CAN 600 or other proposed regulatory compliance issues.

Changes forthcoming under NSF/ANSI/CAN 600 also apply to potable water transmission pipelines, which will need to be lined with approved materials. phOTO: COURTESY OF the sherwin-williams company

Meeting Guidelines Early

As final adjustments to the NSF/ANSI/CAN 600 standard are locked in and its implementation bubbles to the surface, the industry will have a better idea of what coating and lining systems will be approved for potable water use beginning in January 2023. All signs point to a major reduction in the use of solvented, thin-film epoxies in favor of high-build, 100% volume solids formulations — with that reduction being more drastic if oxsol is no longer an exempt solvent. Owners, engineers and applicators will be best served by switching to approved systems early to not only ensure compliance with the new standard, but to also overcome the learning curve related to using plural-component spraying equipment.

Fortunately, a growing number of 100% volume solids materials are being approved for use under NSF/ANSI/CAN 600, with at least one lower-volume solids formulation ready for use today, and into the future. In addition, polyurethane linings are viable options that already meet the NSF/ANSI/CAN 600 standard. Applicators can use these 100% solids polyurethanes nearly at will, but they should consider a number of variables, such as the application location, environmental exposures and service con­ditions, to determine if an epoxy would be a better choice.

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