Volume 43 Number 10
Bottled Water Filters: A Class of Their Own
ANSI/NSF Standard 53 covers water treatment units and the evaluation of those products’ capability to remove health-related contaminants from drinking water. Under the standard, there are two main types of certification—the complete system and the components. A complete system is defined as a complete water treatment device, including all components needed to connect it to a potable water supply. These products are capable of obtaining a number of contaminant reduction claims as detailed in the standard.
Components, on the other hand, can be certified to the standard and can only be listed for material extraction and—if a pressure-bearing component exists—structural integrity. The standard, as currently written, doesn’t allow for components to claim any reduction capabilities for a number of reasons.
Fitting the bill
For example, a filter capable of obtaining a 1,000-gallon capacity for volatile organic compound (VOC) reduction at 0.5 gallons per minute (gpm) may not be able to meet the same capacity of a system that has a flow rate of 1.0 gpm. This is why it’s critical to use only replacement elements as specified by the certified system.
Likewise, a filter certified as a component cannot be listed for any reduction claims since it hasn’t been evaluated within a defined housing. Just because a filter looks like it will fit into a “standard” housing doesn’t mean that it will function or seal properly. A housing and cartridge must be designed to fit each other in order to obtain the reduction performance as stated on the data plate.
Exceptions to the rule
In 1997, the bottled water industry came to NSF with a concern and a request. They had been getting a lot of pressure from their consumers to prove that their bottled water didn’t contain Cryptosporidium. Consumers wanted testing through a third-party laboratory. Upon this increase in consumer awareness, the bottled water industry went to the filter manufacturers and asked if they had third-party testing to prove their filters removed Cryptosporidium. The bottled water filter manufacturers and the bottled water industry then came to NSF to develop a certification for these types of filters. The Drinking Water Treatment Unit (DWTU) Joint Committee agreed to work with the industry in order to provide answers for its consumers.
A filter meeting the dimensional requirements of a “222” or “226” cartridge is specifically designed to fit into a filter cup and housing designed to hold those filters. As developed, only filters that have a redundant filtration element sealing mechanism such as the 222 and 226 double o-ring seals are capable of being tested. These filters can have different locking mechanisms; however, the double o-ring and the 222-mm and 226-mm top dimension remains standard. Since this industry standard already exists, replacement elements for these standard cups and housings can be certified.
Road to certification
The task group identified that the testing protocol would have to be different than the protocol used for Cryptosporidium removal for other point-of-use/point-of entry (POU/POE) systems. Unlike a household unit where the system would see a constant inlet pressure—and as the filter is plugged up with particles, the flow rate would be reduced—bottling water plants have a specific production rate that they must maintain. For bottled water plants, as the filter plugs up, the pressure delivered to the filter is increased in order to maintain the desired gpm for production goals.
With this in mind, the task group worked out a system where the filter would initially see the rated service flow of the filter as specified by the manufacturer. The manufacturer’s rated service flow is then maintained throughout the test. Samples are collected at the start up—25, 50, 75, 100 and 150 percent of the manufacturer’s recommended maximum pressure drop at the rated service flow. Currently, the standard has a maximum pressure drop capacity of 90 pounds per square inch (psi). Therefore, the maximum pressure differential allowed under the standard is 60 psi. With this in mind, a bottled water filter with a rated maximum pressure drop of 60 psi contains samples that will be collected at start up, 15, 30, 45, 60 and 90 psi. Additionally, immediately prior to collection of the effluent samples, a pressure pulse is administered to the system. This is meant to replicate the usage patterns of a filter such as in a bottling plant when operating a fast-acting fill valve. This also provides additional stress on the filter media, which may cause a release of microsphere particles.
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