Pictured is the US Water Filter - Raptor System (Commercial Reverse Osmosis Unit)

In the USA, there are really no specific federal standards related to the sale and use of point of use filters, residential water treatment system, or other systems that serve private water systems. So organizations like The American National Standards Institute (ANSI), the National Sanitation Foundation/ NSF International  (NSF), The American Society of Mechanical Engineers (ASME), CSA Group (CSA), IAPMO Group ( International Association of Plumbing and Mechanical Officials (IAPMO), Canada -Certification/Testing/Standards), Water Quality Association (WQA) and other organizations have developed voluntary certification procedures and processes to ensure the performance of these types of systems for the commercial market. In some cases, the same NSF standard may apply to a public water supply system. and the certification can relate to the safety and durability of the equipment, filter media, and the treatment system or filter performance. 

American National Standards Institute (ANSI)

The American National Standards Institute (ANSI) provides accreditation to companies that manufacture a broad range of products, including water filters and provides a listing of standards of practice for industry and manufacturing. ANSI has over 100 publishers of standards and more than 180,000 titles to choose from pertaining to software, training, industrial supplies, consulting services, acoustical devices, construction equipment, dairy and livestock production, energy distribution, homeland security, smart grid, and social responsibility. ANSI is also actively engaged in accrediting programs that assess conformance to standards – including globally-recognized cross-sector programs such as the ISO 9000 (quality management) and ISO 14000 (environmental management).

NSF International

The NSF International “is a global leader in public health standards, testing, certification, and consulting for various sectors. Learn how NSF can help you improve human and planet health with its services and standard”.  “NSF International provides certification and registration services for various products and systems in different sectors, such as food, water, health, and environment and NSF operates in 180 countries and is a WHO Collaborating Center on Food Safety, Water Quality and Medical Device Safety." (Source)

International Association of Plumbing and Mechanical Officials (IAPMO)

To protect people everywhere through the development and enforcement of safe and efficient codes and standards, and the proper installation of certified products, systems, and materials.....To advance the industries that we serve by delivering world-class education, professional credentials, and related services in cooperation with industry partners." (Source)

Durability and Construction

NSF/ANSI/CAN 61 is a public consensus standard, which establishes minimum criteria for evaluating the health effects of materials, components, products, and systems in contact with drinking water which includes the filter material.  Products can be both tested and certified against the standard’s benchmarks.

NSF/ANSI 24: Plumbing System Components for Recreational Vehicles

ASME A112.19.3/CSA B45.4: Stainless Steel Plumbing Fixtures

Most Common Certifications for Residential Applications.

Many commercial water filtration systems meet one of more of the following performance standards NSF/ANSI 42 (aesthetic quality of the water), 53 (health related contaminants like lead and forever chemicals), 401 (emerging chemicals), P473 (PFOA/PFOS - Old standard), and 61 (System components and filter media) and some specialty water treatment apparatus meet NSF/ANSI 55 (UV Disinfection), 58 (Reverse Osmosis- includes forever chemicals), and 62 (Distillation System).

NSF/ANSI 42

Filters and systems are certified to reduce aesthetic impurities such as chlorine, taste issues, and odor issues. The systems include point of use device, whole house water treatment systems, and even water pitchers.  In most cases, the standard assumes that the water has already been treated to make the water drinkable.  These can be point-of-use (under the sink, water pitcher, etc.) or point-of-entry (whole house) treatment systems.  Products can be certified if the products meet certain benchmarks and performance criteria set by NSF/ANSI for each contaminant.

NSF/ANSI 53

This standard is related to the water filter or water filtration systems ability to reduce a contaminant that has a health impact or concern.  The process assumes that the water already meets drinking water standards and the system is providing a means to “polish” the water.   This contaminants of concern can include nitrate, fluoride, arsenic, lead, mercury, and even pathogens.  

NSF/ANSI 61

This standard "was developed to establish minimum requirements for the control of potential adverse human health effects from products that contact drinking water."  It does not relate to the performance of the system. 

For the most part, you are looking for a water treatment system or a filter within the water system that  meets NSF/ANSI 42, 53, and/or 61.   

Specialty Certifications

NSF/ANSI 44

This is a standard that is specifically related to drinking water systems that reduce the hardness of the water, aid in controlling scale formation, and remove other contaminants, such as trace metals from the water.  The standard relates to systems that use an ion exchange approach to water treatment, such as a water softener.   Water softeners use a cation exchange resin that is regenerated with sodium or potassium chloride. The softener reduces hardness caused by calcium and magnesium ions and replaces them with sodium or potassium ions and helps to reduce scale buildup in piping and equipment.

NSF/ANSI 55

There are two types of Ultraviolet water treatment systems, Class A and Class B.  Class A Ultraviolet treatment systems are designed for water that has not been pre-treated and may have a problem with total coliform, E. coli., or other viruses and pathogens.   The system is designed to inactivate these pathogens and typically the system has prefiltration and post-filtration.  A Class B ultraviolet system should be used on partially treated water to reduce and control bacteria that is not typically associated with disease, such as heterotrophic bacteria, standard plate count, and some nuisance bacteria.   If you water is positive for total coliform, the solution is not the installation of a Class B Ultraviolet treatment system, but if you are on city water that has been treated a Class B Ultraviolet treatment system may be a solid barrier for your home and family. 

NSF/ANSI 58

This standard relates to the use of Reverse Osmosis water treatment systems. Reverse osmosis (RO) systems are frequently used to reduce the levels of total dissolved solids and suspended particles within water. There are some contaminants not removed from water by RO systems. Reverse osmosis units do not effectively remove most organic compounds, bacterial microorganisms, chlorine by-products, or dissolved gases like carbon dioxide, methane, and radon. Reverse osmosis systems use pressure and a semi-permeable membrane to push water through a membrane and therefore leaving behind the suspended particles and the contaminants.  RO systems typically require some form of pre-treatment and post-treatment.   The most common type of most treatment is a remineralizer to give the water a crisp taste.  The effectiveness and efficiency of an RO system can be improved by adding a booster pump and permeate pump to the system. The reverse osmosis booster pump increases the water pressure in the feed line, while the permeate pump does not increase pressure, but helps the reverse osmosis unit waste less water.

NSF/ANSI 62

This standard relates to the process of distillation and distillation systems. Distillation is not a common water treatment system used for private wells or private water systems (it’s expensive). In water distillation, it is typically advisable to provide some pretreatment that may include particle filtration, water softening, and possibly post-filtration using an activated-carbon block filter. Distillation requires heating the water to the point of creating a water vapor, i.e., boiling, and then cooling the vapor to produce a 99.9%+ pure water. Vacuum distillation can be used to cause the water to initially evaporate.  In distillation water treatment systems, the water is heated to the boiling point and then the water vapor is allowed to condense.  The condensate is the purified water because all the dissolved salts and contaminants are left behind in the evaporation chamber.   This process is not 100% effective against contaminants that can volatile or in a gas state, since these contaminants may become part of the water vapor.  For this reason, the distillation system should have some form of pretreatment to manage these contaminants.  

NSF/ANSI 177

This is a standard related to shower filters that are designed to remove the free chlorine from the water using a KDF media.  If you are getting green hair when you go swimming, it is possible that the chlorine in the pool water is reacting with the copper in the water to create copper oxides that are then combining with the protein in the hair.  Individuals typically utilize these systems because they are concerned that the chlorine in water may also strip some of the natural oils from the skin and the chlorine in the water may leave behind a chlorine smell or effect color treated hair.

NSF/ANSI 401

Treatment systems for emerging contaminants include both point-of-use and point-of-entry systems that have been verified to reduce one or more of 15 emerging contaminants from drinking water. These emerging contaminants can be pharmaceuticals or chemicals and include Meprobamate, Phenytoin, Atenolol, Carbamazepine, TCEP,  TCPP, DEET, Metolachlor, Trimethoprim, Ibuprofen, Naproxen, Estrone, Bisphenol A, Linuron, and Nonyl phenol. Because of some of the costs associated with testing for these contaminants, it may be more cost-effective to simply utilize a point-of-use system that provides a proactive barrier.

NSF P473 

When concerns related to the forever chemicals, i.e., PFOS and PFOA, were becoming a concern, the response by the certification agencies was to create standard and benchmark NSF-P473.  This standard looked at the effectiveness of "Drinking Water Treatment Units  to  remove PFOS and PFOA to reduce these contaminants to less than 70 parts per trillion (ppt) .  A total of 76 different products by 10 different manufacturers were certified using this protocol.  Because of the changes in the standards, this certification has been replaced by changes to NSF/ANSI 53 and NSF/ANSI 58.

Important Note:

Just because a filter is certified to an NSF/ANSI standard, this does not mean that in all cases and at all contaminants levels the filter will effectively remove the contaminate.   In most cases, the certification process assumes that the water already meets drinking water standards and these systems are providing a proactive barrier to exposure. It is very critical to attempt to establish a clean healthy water source for you and your family and it is important to Get Your Water Tested and to properly maintain these systems. No water filtration system is maintenance free, these systems require maintenance, cleaning, filter changes and to be used as directed.

Additional Resources - 

NSF Certification Look UP (Water).

Treatment Portals

Ultimate RV Filtration System with VirusGuard

US Water Systems - Residential / Commercial
Crystal Quest Residential / Commercial/ Industrial
Filterwater.com

Point of Use Systems

Aquasana on Amazon
Hydroviv - Custom Point of Use Filters