By Rick Andrew
Having recently moved into a home in Michigan that is served by a private well, I have experienced iron-contaminated water firsthand. Even as my wife and I first toured the home during a showing, it was obvious from the red staining in the fixtures that one of the immediate priorities would be installing a treatment system for the iron problem. Once we began regularly using the water, an iron treatment system became imperative. All the fixtures quickly became more deeply iron stained, the familiar rust red color that many private well owners know all too well. Within three weeks, our new iron treatment system was installed.
Iron and manganese are often associated with hard groundwater. Because they are responsible staining fixtures and laundry, these contaminants are a main focus of well water treatment. There are a variety of approaches and techniques to treat well water for iron and manganese. Typically they are somehow oxidized and then filtered from the water. There is also a standard to evaluate and ultimately verify the effectiveness of this type of treatment. When manufacturers work with an independent testing and certification agency to verify performance against standards, buyers have the added confidence that comes with third party-certification.
NSF/ANSI 42 and iron and manganese reduction
One of the challenges of testing for iron and manganese reduction is that these contaminants are found naturally in ‘clear water’ form, meaning the chemically reduced 2+ valence form. Once these ions are oxidized, they are no longer very water soluble. They precipitate out of solution and cause the red or brown discoloration that drives private well owners to seek water treatment options.
The typical approach of mixing up a large tank of water in a laboratory and adding some iron or manganese to the tank for purposes of testing will not really work. The water in the tank would be exposed to air, which contains dissolved oxygen and that would be enough to oxidize the iron and manganese to insoluble form that is much easier to treat. That’s not how these contaminants are found in well water and this approach would lead to an ineffective testing method.
The standard addresses this reality by specifying that the test be conducted using a water source that does not allow the iron or manganese to become oxidized. This is typically a natural well water that already contains iron or manganese. The concentration of iron or manganese present in the challenge water, as well as the concentrations permitted to be in the treated water, are specified in Figure 1. Also, note that a particular test is typically for either manganese reduction or iron reduction, but not both, although testing both at the same time is not prohibited.
Test method for POE systems
For POE systems, the standard specifies that one system be tested after conditioning, per the manufacturer’s instructions, to 100 percent of the manufacturer’s rated treatment capacity, with samples collected after 10 unit volumes and then each 10 percent of capacity until 100 percent is reached. Ninety percent of the treated water samples, including the sample at 100 percent of capacity, must have iron or manganese below the required concentration. Testing is conducted at the manufacturer’s rated service flow, with continuous flow 16 hours per day.
Recognizing that many of these systems do not have manufacturer’s rated treatment capacities, but rather backwash periodically, the standard specifies that systems shall be backwashed at the manufacturer’s recommended interval, with a minimum of one backwash at the midpoint of the test. So, the test is conducted over two operational cycles with a backwash at the midpoint.
Regenerating systems can also be evaluated and must meet the requirements after a minimum of three operating and regeneration cycles. NSF/ANSI 42 also includes requirements for testing iron and manganese reduction on POU systems, including plumbed-in, faucet-mount, pour-through, mouth-drawn and hand-squeezed, should any manufacturers ever want to evaluate these types of products for iron or manganese reduction.
There are additional requirements for systems to conform to NSF/ANSI 42, above and beyond checking the capabilities of the system to treat the water for iron or manganese contamination. These requirements include the following:
• Material safety. An evaluation of the safety of materials in contact with drinking water includes a review of the formulation of each material and a whole-system extraction test to determine what contaminants, if any, may be leaching from the materials. A toxicological assessment of any contaminants that leach is required. Systems that contain active media such as activated carbon are required to be tested with and without the media.
• Structural integrity. Systems are required to undergo two tests, with each test being conducted on a separate sample and a passing result being indicated by the system remaining watertight at the end of the test:
— A hydrostatic pressure test, which is a 15-minute test at 300 psi or three times the manufacturer’s pressure rating, whichever is higher.
— A 100,000 cyclic test in which the pressure is increased to 150 psi and then decreased to < 2 psi 100,000 times.
• Pressure drop and flowrate. POE systems must have a rated service flow of at least 4 gpm, with a clean system pressure drop of no more than 15 psi at the rated service flow.
• Product literature. Systems conforming to NSF/ANSI 42 must include specific information in their installation and operation instructions, in their performance data sheet, on their data plate and on the replacement element packaging (if applicable).
The purpose of the NSF/ANSI Drinking Water Treatment Unit (DWTU) standards is to provide scientifically based American National Standards developed through a consensus process to allow product assurance. By including rigorous but realistic testing requirements representative of conditions encountered in the field that are reproducible in the laboratory, assurance of product quality and performance can be accomplished. The cases of iron reduction and manganese reduction are good examples of this approach to testing methodology.
The inclusion of additional requirements for material safety, structural integrity, pressure drop and product literature provides a well-rounded evaluation assuring a product that will 1) be safe to use, 2) perform to expectations, 3) be unlikely to leak, 4) provide adequate water pressure downstream and 5) provide a thorough explanation of performance and user responsibilities. By pursuing conformance to standards such as NSF/ANSI 42, manufacturers can provide their sales and distribution partners (and ultimately their end customers) the best possible assurance of product quality.
About the author
Rick Andrew is NSF’s Director of Global Business Development–Water Systems. Previously, he served as General Manager of NSF’s Drinking Water Treatment Units (POU/POE), ERS (Protocols) and Biosafety Cabinetry Programs. Andrew has a Bachelor’s Degree in chemistry and an MBA from the University of Michigan. He can be reached at (800) NSF-MARK or email: [email protected]