NSF 350 Explained

NSF 350 – Onsite residential & commercial water reuse systems 

Point Form Explanation: 

  • For treatment components to be regarded as ‘safe’ to use they must have undergone some type of ‘third party testing’ 

  • The third party will take specific equipment (UV disinfection systems, inline filters, Greywater treatment systems) and test them under specific conditions and sign off saying that ‘Yes, this system or component does perform the way the specific NSF standard outlines 

  • NSF is that third party that validates treatment components or equipment and gives it their ‘stamp’ of approval – NSF (National Sanitation Foundation) seal of approval is recognized worldwide but more so in North America 

  • NSF 350 is specifically written for greywater treatment equipment 

  • To test a system, NSF must set up the device as it would be installed in a real-life installation  

  • They also must have a representative influent water that maintains the same characteristics of what we would see in a typical home 

  • Therefore, NSF must create ‘greywater’ in their lab and run it through the Hydraloop device 

  • NSF will be aware of what is in the water going into the device and will test the characteristics of the water coming out of the device 

  • From those results they can determine if the Hydraloop device can deliver reusable water that is what NSF deems ‘safe’ to reuse within the home/facility for toilet flushing, washing machine use and/or outdoor use 

  • During the NSF 350 test the device is actually on test for 26-weeks to get an accurate test length to mirror a real-life installation 

  • This testing period does not just focus on the water quality but also on the loading of the greywater recycling device; this is called stress testing and it can include the introduction of elevated levels of components like soap to the device 

  • The concentration of greywater from showers, baths and washing machines is well documented and NSF has produced the list of characteristics and their concentrations that greywater treatment systems must meet 


Greywater typically has high concentrations of the following: 

  • TSS: total suspended solids – this is a measure of suspended solids in a sample and the concentration (ppm) provides the weight of particulate material that is present in the water.  This parameter would assist in determining what kind of load of particulate would be collected from water.  For example, if there is a high TSS concentration you would know that the load on the filters would be high and therefore the filters would need to be changed more frequently 

  • Turbidity: The cloudiness or haziness of a fluid due to particles visible to the naked eye – turbidity and TSS are essentially the same parameter, but turbidity is more a measure of how well light can pass through a sample whereas TSS is more of a quantitative expression of suspended particles.  Typically, Turbidity is a concern when you are incorporating a UV system.  Turbidity is visible to the naked eye, microorganisms are not.  Consider how many microorganisms can attach themselves to a piece of turbidity and can be shielded when passing by a UV light thereby getting through to the treated water. All turbidity must be removed from the water prior to a UV system. The level of turbidity will assist in determining the size of filter you need.  An elevated level of turbidity (say 10 NTUs) will need a 20-micron filter to remove it whereas a turbidity of say 2 NTUs will only need a 5-micron filter. 


  • BOD: Biological Oxygen Demand – Higher BOD indicates more oxygen is required, which is less for oxygen-demanding species to feed on and signifies lower water quality. And a low BOD means less oxygen is being removed from water, so water is generally more pure 

  • BOD is a biological oxidation & is performed by aerobic organisms (organisms that thrive when oxygen is present) 


  • COD: Chemical Oxygen Demand – The oxygen demand that is consumed by both organic and inorganic matter present in a sample. COD measures the oxygen required to decompose organic and inorganic constituents present in a sample by a chemical reactionIf there is a 'high demand' for oxygen that indicates that there is something in the water depleting, it which is detrimental to the condition of the effluent. 

  • COD is a chemical oxidation process performed by chemical reagents in the sample 

  • Total coliforms: this is a group of bacteria that are not bad for you (non-pathogenic) - this is called an indicator group.  If there is a high level of total coliform then you need to determine what makes this number high by testing for more specific, pathogenic bacteria 

  • E.coli: pathogenic bacteria that indicates that the sample has been exposed to mammal waste. If you have a high total coliform count this usually is an indicator that there is E.coli present