About the author: Ellen Van Buren is an account executive with the NSF DWTU Program. She can be reached at 800.NSF.MARK, or by e-mail at [email protected].
Ellen Van Buren
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NSF currently has more than 2,000 components listed (or certified—these terms are interchangeable) to the drinking water treatment unit (DWTU) standards. Components can be certified under several NSF/ANSI standards, depending on the product’s intended end use. A component is defined as a part or subassembly of a system that must be combined with other components before providing the user with treated water.
Some examples of certified components include filter cartridges, housings, RO elements, faucets, media, fittings, tanks, tubing, valves and many others. All of these are tested and certified for material safety, and those that are pressure bearing are also tested and certified for structural integrity. Table 1 is a quick reference to the categories of components that can be NSF certified, along with the applicable standards and testing requirements for each category. As with the certification of a complete system, component certifications help establish confidence in the safety and quality of the product.
Material Safety Evaluation
All DWTU standards require components to undergo a material safety evaluation, which is composed of a formulation review and extraction testing. This process ensures that the materials in contact with drinking water do not leach levels of contaminants that exceed the Maximum Drinking Water Levels specified in the standards. This is the same process that occurs for all system certifications.
First, the material formulations are reviewed for ingredients, monomers or impurities that could potentially leach into the water and negatively impact the water quality. Next, the extraction testing begins by flushing the product in accordance with the manufacturer’s instructions. The product is then exposed to water under the conditions outlined in the appropriate standard. The exposure and sampling procedure involves filling or immersing the component in exposure water and maintaining it for 24 hours. A water sample is then collected. This procedure is repeated for two more 24-hour periods, using fresh exposure water each time. The three samples are composited, and a full chemical analysis of the composited exposure water sample is conducted based on the formulary review of wetted materials. Any contaminant found in the water must not exceed maximum values, as indicated in each standard.
Structural Integrity Testing
In addition to the material safety evaluation, structural integrity testing is required for all pressure-bearing components. Structural integrity testing is designed to simulate stress on the component over time. Depending on the type of pressure-bearing component, the required structural tests can include hydrostatic pressure, cyclic pressure and burst pressure tests. Each test is conducted using one new (previously untested) sample, such that the same sample does not have to survive a series of tests. Additionally, tests are not carried out to failure of the product, but rather to the end of the prescribed test, where the product must remain intact and without any water leakage.
Hydrostatic pressure testing. Hydrostatic pressure testing simulates a short-term surge in line pressure and verifies the integrity of seals. For the hydrostatic pressure test, the pressure in the component is raised to a maximum pressure prescribed by the standard and held for 15 minutes. The component must remain intact and watertight to pass. For most components, the hydrostatic pressure test is conducted at three times the maximum working pressure, or 300 psig, whichever is greater.
Cyclic pressure testing. Cyclic pressure testing simulates the opening and closing of valves in the overall plumbing system. During this test, the pressure is increased to a specified pressure and then released to less than 2 psig before being increased again for a specified number of cycles. The pressure ramp up must be greater than one second. The total time to complete one cycle is typically less than five seconds. Most components are subjected to 100,000 cycles of 0 to 150 psig pressure. This simulates 27 valve operations per day for 10 years. Disposable components are subjected to 10,000 cycles of 0 to 150 psig pressure, which simulates 27 valve operations per day for one year.
Burst pressure testing. Burst pressure testing involves an instantaneous pressure, then release. Burst testing is required for non-metallic components only. For this test, all openings are closed off, and pressure is increased to 400 psig, or four times the maximum working pressure, whichever is greater. The maximum pressure is held for a brief moment and released. To pass the test, the component must not leak water.
A Valuable Resource
The NSF certified component listings are a valuable resource for system manufacturers in search of components that have been independently verified for their safety and quality. These certified components have the proper material formulations and test data already on file with NSF. Using these pre-qualified components makes the certification process for a new system manufacturer easier and less expensive. Also, certified components can be more easily adapted for use in already-certified systems. These benefits make it easy to see why NSF certified components are the components of choice for drinking water treatment system manufacturers.
