NSF stands for National Sanitation Foundation. NSF has worked hard with manufacturers and consumer groups to create standards for water treatment products targeted for the general consumer. Purchasing a product that has been NSF tested basically means that tests in the NSF lab support the manufacturer's claims about the product. It does not mean that the filter is better than another, or that it will take out all contaminants on any water supply. It simply means that the claims are accurate.
Whenever possible we try to use component parts that have been tested to NSF protocols. However, NSF has not made standards for deionization filters, which are used in our MB Series Filters. Deionization is more commonly used in commercial applications where NSF standards don't apply.
Our Carbon Block filters are not NSF tested because of the huge cost and the limitations it sets on making future improvements. If we make the investment in NSF testing, we will be less likely to make improvements in the filter in the future because of the cost of getting the filter re-tested. We cannot customize systems and have them NSF tested. We prefer the flexibility to alter a filter to meet one customer's needs rather than make a filter one way and never change it again.