By Rick Andrew
Pour-through, gravity fed pitcher filter systems enjoy considerable consumer popularity. Their desirable features include typically relatively low cost, ease of use, wide availability and considerable performance in terms of contaminant reduction capability.
They do have their performance and functional trade-offs for consumers to consider, including issues such as flow rates being lower than typical plumbed-in systems, taking up space in the refrigerator and their filters having a relatively low capacity. But many consumers look more toward the advantages offered by these products and choose pour-through gravity fed pitcher filter systems to suit their needs.
System standards
The operative standards for pour-through pitcher filter systems are NSF/ANSI 42 and 53. These standards have identical requirements for material safety and structural integrity, but cover different types of contaminant reduction performance.
Structural integrity of a pour-through pitcher filter system is a simple concept. Because these products don’t bear the pressure spikes and plumbing system effects of opening and closing of valves the way plumbed-in water treatment systems do, the only requirement for structural integrity of pour-through pitcher filter systems is that they hold water and do not leak under normal operating conditions. No specific test is required, although leakage when conducting other laboratory tests would indicate a structural defect that would result in a non-conformance with this requirement of the standard.
NSF/ANSI 42 addresses reduction of aesthetic contaminants, including those that affect drinking water such as taste, odor, color and appearance, which may in turn affect acceptance of public or private drinking water. NSF/ANSI 53 addresses reduction of contaminants that have known health effects.
Many pour-through pitcher filtration systems are certified to both NSF/ANSI 42 and 53. Certification can be accomplished through testing for material safety, the requirements that these standards have in common and for various claims under both. The claims made on pour-through pitcher filter systems under these standards are entirely at the discretion of the manufacturer and are, of course, also dependent on the filter system to meet the requirements for making the claim.
Chemical reduction
NSF/ANSI 53 defines chemical reduction as “the reduction in the quantity of one or more specified organic or inorganic contaminants in drinking water.” The realm of organic and inorganic contaminants is a very broad one, including such familiar contaminants as chlorine, chloramine, volatile organic contaminants, various pesticides and herbicides and metals including lead.
Chemical reduction involves adsorption and/or absorption by the media in the pour-through pitcher filter. This leads to questions about the capacity of the filter, which is impacted by chemical properties of the contaminant, concentration of the contaminant in the influent water, maximum allowable effluent concentration, contact time with the media as water passes through the filter and system integrity as it is continually operated and inverted by consumers. All of these factors are taken into account in the test methods for chemical reduction in NSF/ANSI 42 and 53.
Testing involves operating the system exactly as a consumer would, following the manufacturer’s recommendation for maximum volume of water treatment per day. This means manual operation of the system by laboratory technicians. Although there can be some variability in the way technicians fill and pour the system, there are guidelines to ensure consistency in critical parameters.
For example, complete batches are processed. The hopper, or untreated water reservoir, is completely filled for each batch. The complete batch is allowed to process prior to beginning a new batch. The succession of one batch after the next is randomized, but is also tracked to ensure that the manufacturer’s maximum recommended daily treatment volume is not exceeded and to ensure that the correct testing volume is achieved.
There has been discussion about developing automated test stands for testing pour-through pitcher filters. This approach could lead to certain advantages, such as potential labor savings, possibly lower testing costs, as well as potentially greater repeatability of tests.
However, the design of the test stand can significantly influence the way the system processes water and could lead to lab results that are not representative of consumer usage. This is a risk.
A simple example of this issue is to consider a ‘drip-through’ type test stand, designed to simply feed influent challenge water into the hopper of the pitcher. The pitcher is modified to allow filtered water to drain out the bottom or to be collected for analysis at sample points. A continuous feed is maintained throughout the test.
This type of test could overstate system performance because it allows loose media beds to compact nicely and remain compacted without potential upsetting of the media bed and/or the introduction of air during an inverting and pouring operation, which occurs in consumer usage. Or, it could understate system performance because of the constant contaminant challenge feed, compared to the batch processing seen in normal consumer usage. In any case, it leads to questions about how representative is this type of consumer usage testing.
Contaminant concentration
The concentration of the contaminant in the influent challenge water under NSF/ANSI 42 is set at a typical value based on occurrence. The concentration of the contaminant in the influent challenge water is typically at the 95th percentile of contaminant occurrence, based on US Geological Survey data or other sources of occurrence data.
This means that 95 percent of those water sources identified to be contaminated with the chemical in question should have a concentration equal to or lower than the challenge concentration used in the standard. When this method suggests a low concentration, or when occurrence data is not available, a concentration of three times the maximum allowable effluent concentration is used.
For aesthetic contaminants under NSF/ANSI 42, the maximum is set based on US EPA secondary maximum contaminant levels or other aesthetic thresholds. The maximum allowable effluent concentration for health contaminants under NSF/ANSI 53 is set at regulated levels based on US EPA or Health Canada limits, or at other health effects concentrations when contaminants are not regulated by these agencies.
Samples of the influent and effluent water are collected at specified intervals throughout the test, typically at six different sample points. Performance for aesthetic contaminants under NSF/ANSI 42 must be acceptable to 100 percent of the manufacturer’s rated capacity based on volume.
Performance for health contaminants under NSF/ANSI 53 must be acceptable to 200 percent of the manufacturer’s rated capacity based on volume. For those systems incorporating a performance indication device, which is a volume-based filter change indicator, performance must be acceptable to 120 percent of the manufacturer’s rated capacity based on volume.
Appropriate test methods
Gravity-fed, pour-through filtration systems are popular with many consumers for a variety of reasons. They can also have a broad range of contaminant reduction performance.
Some of them have multi-media filters capable of reducing the concentration of both aesthetic and health contaminants. These contaminants include chlorine taste and odor, organics and inorganics, including metals such as mercury and lead.
When testing these products, it is important to ensure that test results in the laboratory are indicative of usage by consumers. Although it is tempting and interesting to automate the contaminant reduction testing process for pour-through filters, doing so while maintaining conditions that simulate consumer usage is a complicated endeavor.
Consumers introduce water to the pitcher’s hopper from their tap, then allow the system to process water, pick up the pitcher and invert it to pour water out and set the pitcher back down. All of these various motions introduce variables into system operation that are difficult to account for with automated test stands.
For this reason, the current state of the art in testing pour-through pitchers is the brute force approach of laboratory technicians, operating the pitcher exactly as does a consumer.
About the author
Rick Andrew is the Operations Manager of the NSF Drinking Water Treatment Units Program. Prior to joining NSF, his previous experience was in the area of analytical and environmental chemistry consulting. Andrew has a bachelor’s degree in chemistry and an MBA from the University of Michigan. He can be reached at 1-800-NSF-MARK or email: [email protected].