Demystifying NSF/ANSI standards for water filters (part 3): standard 42

Continuing from my earlier 2 posts (1, 2) on NSF/ANSI standard 42, here's the meat in describing this commonly encountered standard for "drinking water treatment unit" (read water filters).


If you are the lucky few who have a copy of the document, it certainly makes for good bedtime reading i.e. getting you to sleep. Therefore, I will try to be short and sweet in this post.


Even though the title of this standard states "aesthetic effects", it actually covers quite a lot of details in a water filter, and not just how well the filter works in improving the aesthetics of drinking water.


The standard apparently can apply to a "system" (e.g. entire filter unit) or a "component" (a single part of a filter unit). I assume my readers are more interested in evaluating an entire system so I shall focus my discussion on a "system". (This decision is also a conservative measure since the requirements for a component are less stringent than for a system.) Buyers beware: make sure the standard covers the whole filter system you are buying, and not just certain components inside.


To be certified, a filter system must satisfy the five following conditions.

1. System materials in contact with drinking water must not leach chemicals into the water within specific limits. Chemicals to be tested include aluminium, mercury, vinyl chloride, xylenes and many others. Much is described about how testing is done and the chemicals of concern.
   
   In other words, you don't want to buy a filter that adds poisons into your drinking water. With such a filter, you don't need poor filtration effectiveness to harm yourself.
2. Structural integrityThis part talks about pressure testing the materials, design and fabrication quality of the complete system. Basically, your system should not fail (burst, leak) under specific conditions.
3. Minimum performance requirementsThis slightly misleading title actually refers to mundane matters not covered in the other 4 criteria e.g.
1. Minimum service flow rates to be achieved under different configurations
2. Electrical safety and operation complying with National Electrical Code or equivalent.
3. Filter media (e.g. activated carbon) should not migrate visibly (read leak out of the filter).
4. A few other requirements
4. Reduction ClaimsThis is most often mentioned aspect of standard 42, whether by filter suppliers or customers - how the filter reduces the concentration of a certain substance in water.
   
   Buyers beware! This requirement is potentially the one most likely to confuse a consumer on the effectiveness of a filter. To be certified, a filter has to fulfil a reduction claim of ONLY ONE substance. Make sure you know which substance that is. ABC filter certified to reduce the concentration of only chloramines will have unknown effectiveness against chlorine.
   
   Again, please remember that standard 42 is designed to certify a filter for improving aesthetic effects e.g. taste, odour, colour. It is not designed for the removal of adverse health effects e.g. heavy metals, pesticides. You have to look to standard 53 for that.Substances of concern under standard 42 include:
   Bacteriostatic (NOT killing bacteria but keeping bacteria levels more or less the same before and after filtration),
   Chloramine reduction,
   Chlorine reduction,
   Hydrogen sulphide reduction,
   Phenol reduction,
   Particulate reduction (there are 6 classes denoting different particulate size ranges so do check out which class is being certified),
   a few more other parameters e.g. iron, zinc, manganese
   
   Again, we see the usual descriptions of testing methods and influent challenge (i.e. the characteristics of the inflow into the filter)
   
   Here is an example of the reduction requirement for chloramine:
   Average influent (aka inflow) challenge concentration: 3.0 mg/L +/- 10%
   Reduction requirement: 0.5 mg/L (meaning the outflow should have a concentration of 0.5mg/L or less)
5. Instruction and installation
1. Details must be provided for installation, operation and maintenance
2. Some other details
3. And easily as important as the reduction claims, a performance data sheet must be available to potential buyers
   
   Buyers' tip! Scrutinise the performance data sheet. (Some filters not certified under this standard may have it too.) It may look discouragingly technical but it should look similar to the following example. (Influent challenge refers to the test sample going into the filter while product water refers to the outflow from the filter.)
   
   Obviously, if the filtered is certified, its performance should equate or exceed that of the standard.

Sample Performance data sheet reduction claims
Substance	influent challenge concentration	maximum permissible product water concentration
Chloramine	3.0mg/L ± 10%	0.5mg/L
Iron	3-5mg/L	0.3mg/L
foaming agent	5mg/L ± 10%	0.5mg/L

Believe me, I have really tried to simplify NSF/ANSI standard 42 in these 3 posts as much as possible for the layperson. Hopefully, you now have a clearer idea what this standard is all about.


Good luck!

Figure: A few rare filter housings I have seen

The must-have resource for the rainwater harvester

If anyone out there feels like setting up their personal rainwater harvesting (RWH) system, this is a must-have book.

Rainwater Collection of the Mechanically Challenged by Suzy Banks and Richard Heinichen

I came across this when I was working on my RWH project and found it immense useful, especially for the DIY homeowner.

Written for the layperson (that included me when I first started out on RWH), it is simple to read. It doesn't bore you down with details. Instead, it gets straight to the point of setting up your RWH system, supplemented with simple diagrams that anyone can follow and implement.

Though designed for the DIY homeowner, it is also useful to help you know what you are getting into even if you intend to let a contactor handle the installation.

I especially like the section on sizing your rainwater storage tank. (Yes, you do need a storage tank for RWH and this will take up the most space.) It is clear and the mathematics simple. I can hardly find similar information elsewhere.

There is a section on troubleshooting which will come in handy when (not if) you encounter operational problems.

Of course, its strength and limitation is the assumption that you are living on landed property. Its ideas are based on the private home setup. For example, the setup is based on using the roof as the collection receptacle and gutters to pipe the rainwater for storage. If you are installing RWH elsewhere e.g. industrial/commercial buildings, this book does not offer alternatives so you have to read up more and customise accordingly.

Essentially, their setup is made up of:
(The order below follows the flow of rain on the roof all the way to the tap.)

1. Roof
2. Gutters
3. First flush diverter
4. Storage tank
5. Pump (+ electrical components)
6. Pressure tank (+ electrical components)
7. Filters

* The above are linked with piping, fittings and valves. The authors are proponents of PVC piping so no other alternatives are discussed.

The book discusses concisely and clearly how to set up the above components to make them work as an efficient whole. I find their descriptions adequate for you to go down to the bolts and nuts on  your own but yet not excessive that you are overwhelmed by indecision leading to inaction.

Besides the landed property assumption mentioned above, do note that the setting in the book is based on Texas in USA. If you are from another state or country, obviously, you have to double check your local laws on RWH which may or may not coincide with what the authors suggest.

For those in Singapore, it is mandatory to read the following:

1. PUB Guidance notes for the application of rainwater collection systems
2. NEA guidelines on mosquito prevention in domestic rainwater collection system for non-potable uses

A couple of highlights from the above 2 documents

1. The application to PUB for a RWH system has to be lodged by a qualified person (PE or architect). Unless you are a QP yourself, be prepared to engage one (with a budget for his fees) to apply on your behalf.
2. If you are going to use gutters, your application will be routed to NEA for its approval too. And they have certain guidelines for your gutter design to comply with.

Good luck!

Demystifying NSF/ANSI standards for water filters (part 2)

Hi folks,

This is an addendum to my earlier post, Demystifying NSF/ANSI standards for water filters (part 1)

NSF/ANSI certification
I mentioned about checking for NSF/ANSI certification on your product. One way is to look for the NSF mark on your product, packaging and/or documentation. It may look like this:

Figure from NSF

Figure from NSF

1. Do note that that the words on the mark may differ. Besides the above 2 examples, you may see "certified for home use" and other phrases being used.
2. The actual standard is not necessarily shown on the mark e.g. NSF/ANSI 42, NSF/ANSI 53. You will have to check the packaging or dig through the documentation for that.
3. The letters "NSF", white circle and blue leaf background seem quite standard but expect to see variations e.g. the following personal product is compliant to NSF/ANSI Standard 305 

   

   Figure from NSF

 NSF Certified vs. “Tested to NSF Standards”
 One more thing - be careful of products that claim to be "tested to NSF standards". It is meaningless as it is not really certified under NSF, hence there is no guarantee at all regarding its performance. see NSF for more details.

NSF certification has to be renewed yearly by the way.

Apparently, no anyone can perform the testing for certification. The ONLY three certifying organisations are NSF International, WQA (Water Quality Association) and UL (Underwriters Laboratories). 

Stay safe.