By Rick Andrew

One of the tenets of American consumer business dating back to the early 1800s was that of caveat emptor, or buyer beware.1 This essentially meant the buyer had absolutely no guarantee for the quality of goods, and assumed all risk of the purchase. As consumer law has evolved in the US, there have been some statutory laws enacted to increase consumer protection above this essentially non-existent level. For example, many jurisdictions now require that goods be of merchantable quality, which is, in effect, an implied warranty meaning that the goods must conform to an ordinary buyer’s expectations.

This concept of an ordinary buyer’s expectations can be difficult to interpret and also potentially difficult to enforce for specific categories of goods. The difficulty often comes in determining what constitutes an ordinary buyer’s expectations. They may have different levels of product knowledge or experience with the particular type of product involved, or simply may have different inherent standards of acceptance, leading to different expectations.

These consumer laws and their interpretation affect manufacturers and sellers of products as well as consumers. It is difficult for them to operate when the rules are vague and when violation of those rules could significantly impact them. This is one of the reasons why these groups often come together to develop consensus product standards. These standards can help define the product characteristics that would conform to an ordinary buyer’s expectations.

Origin of the standards
In the US in the late 1960s, there was significant activity in the manufacturing and selling of residential POU and POE drinking water treatment products. With no product standards in place, there was wide variation in the basis that manufacturers used to substantiate claims. Some were much more conservative than others, which led to some manufacturers making claims that others felt were not justified.

Similarly, there were different views on material safety for drinking water contact. Some products were bonded with solvents that by today’s standards would not be appropriate for drinking water contact. There were other issues, too.

Given these issues, the water treatment industry, the regulatory community and consumers of water treatment products came together under the auspices of NSF to develop the NSF/ANSI DWTU Standards. The first of these, NSF/ANSI 42, was initially published in 1973; others followed thereafter. They have continued to evolve as technology and the regulatory environment has changed, to the degree that today they are the most comprehensive and conservative POU/POE product standards in the world.

Consumer protection
There are many aspects of POU/POE products that are addressed in the standards, many of which involve setting an ordinary buyer’s expectations and consumer protection. Some are obvious and you may already be aware of them; others are less well known but established to help protect consumers. They include:

  • Contaminant reduction claims. As mentioned above, creating requirements and criteria for making contaminant reduction claims was one of the primary drivers behind developing the standards. Today, there are hundreds of possible contaminant reduction claims for diverse technologies, including carbon filters, mechanical filters, RO systems, ion exchange, UV systems, distillers and shower filters.
  • Material safety. Another fundamental issue behind development of the NSF/ANSI DWTU Standards is an in-depth evaluation of material safety for those materials in contact with drinking water. Consumers can be assured that products conforming to these standards are safe to use and will not adversely affect drinking water quality.
  • Structural integrity. Consumers are protected from costly water leaks by tests of structural integrity that require products to remain water tight when pushed to pressures much higher than typical line pressure, and when cycled from low to high pressure repeatedly to simulate years of usage.
  • Product literature. Essential information must be communicated to purchasers both before and after purchase for products that conform to these standards. Warranty information, availability of replacement parts, operating specifications, clarifications regarding performance, manufacturer contact details and other valuable data are required to be spelled out. Performance data sheets must be available to consumers as a pre- purchase item, whereas data plates must be permanently affixed to the system. Detailed installation and operation instructions must come with the system, and replacement element packaging must identify which system(s) they fit.
  • Replacement elements. The standards require that replacement elements must be readily removable, which means they must be replaceable without the use of special tools. The exception to this would be filter housings that require a special wrench supplied with the filter system in order to loosen them.
  • Hazards. All components must be free of nonfunctional rough or sharp edges, or other hazards that may cause injury to persons adjusting, servicing or using the system.
  • Minimum service flow/pressure drop. POU filtration systems must meet certain minimum flow rate requirements based on product configuration to ensure that consumer expectations are met. A notable exception to this is refrigerator filters, which are exempt from this requirement (see Figure 1). POE systems (except UV systems) are limited in the amount of allowed pressure drop so water pressure and flow rate throughout the home are not unacceptably reduced by installation of the system. Their pressure drop may not exceed 15 psi at the rated service flow, which must be at least four gpm (15 L/m).
  • Filter media. Filtration systems must not release media into the treated water.

Protection for all
Clear rules and guidelines are keys to successful commerce. Operating under vague requirements, such as merchantable quality, can lead to differences in interpretation, which are often resolved by the court system, and can be expensive and time consuming. As a desirable alternative, product standards can help establish an ordinary buyer’s expectations for a particular type of product.

The NSF/ANSI DWTU Standards do just that. By selling POU/POE products that conform to these standards, dealers, manufacturers, consumers and retailers are all protected. Products that conform to these standards may be less likely to be returned, and may be more likely to result in happy purchasers who recommend the products to friends and others in their network.

Independent certification of products to these standards is the clearest and most definitive mechanism for manufacturers to establish conformance of their products. Because certification goes above and beyond in-house testing—or even beyond testing at an independent laboratory—dealers, retailer and consumers can have the utmost level of confidence in their decision to purchase an independently certified product.


  1. Laidlaw v. Organ, a decision written in 1817 by Chief Justice John Marshall, is believed by scholars to have been the first U.S. Supreme Court case which laid down the rule of caveat emptor in US law.

About the author
Rick Andrew is the Operations Manager of the NSF Drinking Water Treatment Units Program for certification of POU/POE systems and components. 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 (800) NSF-MARK or email:


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