NSF Filter Certification

NSF (established as the National Sanitation Foundation) International is an independent organisation, founded in 1944, set up for testing products that affect water quality and food safety. The organisation now known as NSF International has offices around the world with a head office in Michigan USA. NSF is recognised as a leading world authority in the development of standards and testing of water filtration products. These comprehensive standards provide the basis by which product manufacturers can demonstrate the quality, reliability and performance of their products, and through which buyers and consumers can be assured of their safety and benefits. If products pass testing procedures they are certified and can then use the NSF logo and mark.

Why is NSF Certification Important:

Consumers buy water treatment systems for any number of reasons. Maybe they are looking for a system that will reduce unpleasant taste, odour or discolouration in their water, or perhaps they need a system that can reduce harmful contaminants, like lead or microbiological cysts. NSF has developed standards, certification and testing programs in order to give assurance that the system will do what the manufacturer/supply claims it will do.

NSF certification guarantees (through testing) that:

  • The system is able to reduce the contaminants claimed by the manufacturer;
  • The system is structurally sound and it doesn’t add harmful substances to the water;
  • Advertising, product literature and product labelling do not contain false or misleading information;
  • The production facility undergoes annual unannounced inspections by NSF and each model is periodically retested.

NSF standards:

Each NSF standard is technology or system specific i.e. Cartridge filter systems have a different standard to Reverse Osmosis Systems and Shower Filter Systems. Following are the standards applicable to each type of system and technology.
Product Type Contaminant Reduction Claims Standard
Carbon, ceramic or other filter system Aesthetic – chlorine reduction particulate reduction, chloramines reduction, etc. 42
Carbon, ceramic, or other filter system Health – lead reduction cyst reduction, VOC reduction, etc. 53
Reverse osmosis System TDS reduction (mandatory), health claims – lead reduction, cyst reduction, VOC reduction, etc 58
Ultra-Violet system Disinfection 55
Distillation TDS reduction (mandatory) health claims – Lead reduction, cyst reduction, VOC reduction, etc. 62
Water softener system Hardness reduction (mandatory) health claims – barium reduction, radium reduction 44
Shower filter system Free available chlorine reduction 177

Water filtration systems certified under NSF standards are tested in the following ways:

Materials safety evaluation: the specific components used in the system that come in contact with water are checked for ingredients, monomers or impurities that could potentially leach into the water and negatively impact on the water quality. This is performed by NSF’s expert toxicologists. Structural integrity: this pressure tests the specific components and systems. They are tested to remain in tact without leaks at 3 times the operating pressure or 2,067 kpa whichever is the greater.

NSF/ANSI 42-2009

This certification standard covers the performance of the filtration system components and the filter or filter cartridges themselves. It establishes the minimum performance requirements of drinking water treatment filter systems to reduce specific aesthetic (taste and odour) related contaminants. These non-health related contaminate reduction claims include chlorine and particle reduction. The most common technology addressed by standard 42 is carbon filtration.

NSF/ANSI 53-2009

This standard covers the performance of the filtration system components and the filter or filter cartridges themselves. It establishes the minimum performance requirements of drinking water filter/treatment systems to reduce health related contaminants such as lead, cysts, VOC’s etc. The most common technology addressed by standard 53 is carbon filtration. Some products fall under both standard 42 and 53 because they claim a combination of aesthetic and health claims.

NSF/ANSI 55-2009

This standard establishes the minimum requirements for the certification of ultra-violet (UV) light systems. The standard includes material safety, structural integrity, product literature and UV performance.

The UV Systems are categorised either as:

CLASS A: delivers 40 mj/cm² UV dose and has a lamp fail alarm. Class A systems may claim to disinfect water that may be contaminated with pathogenic bacteria, viruses, cryptosporidium or giardia. CLASS B: delivers 16 mj/cm2. Class B Systems may claim to reduce normally occurring nuisance micro-organisms.

NSF/ANSI 58-2009

Standard 58 establishes the minimum requirements for the certification of point of use (POU) reverse osmosis filter systems. The standard includes materials used, structural integrity and safety, product literature, total dissolved solids (TDS) reduction and additional contaminant reduction claims. These additional contaminant reduction claims may include cyst, barium, radium 226/228, copper, hexavalent and trivalent chromium, arsenic, nitrate/nitrite, cadmium and lead reduction.


Standard 177 establishes the minimum requirements for the certification of residential shower filter systems. The standard includes materials used, structural integrity and safety, product literature and free available chlorine reduction. They are also cyclic tested for leaks. Most systems are subject to 100,000 cycles where the pressure is increased to approximately 1,000 kpa then back down to 10 kpa then back up to 1,000 kpa, then back down again, 100,000 times. Burst tests are then carried out on all non-metallic components up to 4 times the maximum operating pressure or 2,750 kpa whichever is the greater. To pass, the components must not leak water.

General Testing

Contaminate Reduction: this testing is done under standard 42 and 53 and includes
  • Chemical reduction:- chlorine, VOC, pesticides, herbicides, metals, etc.
  • Mechanical reduction: - cyst, turbidity, asbestos, particles, etc.

Two filters are used for each contaminant to be tested and both units must pass the test in order to successfully meet the requirements of the standard. Chemical reduction testing is based on the estimated or published capacity of the filter cartridge. For standard 42 the cartridge is tested to 120% of capacity if the system has a performance monitoring device or 200% if not. Testing beyond 100% of capacity is for health related claims only and provides for an additional safety factor if the user does not properly maintain the system as per the manufacturer’s instructions. Regardless of the tested capacity, the manufacturer can only claim 100% of capacity, i.e. if a filter has an NF 53 lead reduction claim for 1,000 litres, it will be tested for 2,000 litres. The filter must reduce lead to the requirements of the standard for 2,000 litres. If the product is able to meet this test requirement, then the product will be certified as providing 1,000 litres of lead reduction. Metal contaminants (lead, etc) tested under standard 53 must be tested at two different pH levels; 6.5 and 8.5. Both these levels must be passed to be certified. Under standard 53 only the contaminant requested by the manufacturer will be tested and certified. A water filter may be certified under standard 53 to reduce one or several contaminants.

Mechanical reduction testing is not based on capacity but rather a reduction in flow rate over the period of the test. Samples are collected at several points of flow reduction, based on a percentage of the initial flow rate with the final sample point being 75% reduction in initial flow rate or 50% reduction in flow for particulate reduction. Testing under standard 53 for mains connected or plumbed in systems is conducted with on/off cycling to simulate the opening and closing of faucet valves and the stopping and starting of flow through the system. For mechanical reduction tests, the cycle is 50% on and 50% off (50/50) or an equal amount of time with flow and without flow. For chemical reduction tests the cycle is either (50/50 or 10/90; 10% on, 90% off, as decided by the manufacturer. In either case, the maximum time for a total cycle is 40 minutes with a minimum of 15 minutes.

Reverse Osmosis System Testing is done under standard 58. This requires RO systems to be tested and certified for the reduction of total dissolved solids (TDS). These systems are tested for 7 days and include measurement of the systems daily purified water output, wastage and efficiency. Other contaminant claims can be tested at the manufacturer’s request. All testing of RO systems is performed after removal of any pre and post filters, so performance is based on the RO membrane. Two RO units must be used for all testing and both units must pass to meet the requirements of the standard. All certified product and system manufactures are inspected during the course of initial certification to verify manufacturing consistency. Once certified, unannounced annual inspections are performed. These inspections include review of inventory records, parts and material verification, product documentation reports, manufacturing walk through, quality assurance documentation review and the use of marking on products and literature. Any problems or variances must then be corrected in a timely manner. Product retesting is then required at five year intervals for continued certification. Any changes made to products after certification need to be authorised by NSF with re-evaluation or further testing required in many cases.