Testing for Scale

July 26, 2021

The long-awaited scale-reduction performance standard is complete

About the author:

Tom Palkon is ASSE executive director for IAPMO. Palkcon can be reached at [email protected]

For decades, the water treatment industry has struggled to quantify the effectiveness of scale reducing devices other than ion exchange water softeners. In 1959, the Water Quality Assn. published the first version of the S-100 Standard that was used as the basis for the current NSF/ANSI Standard 44 that verifies cation exchange water softeners’ ability to reduce water hardness. Since this time, technology has been developed that claims to reduce scale formation in plumbing systems without reducing the hardness ions from the water. As this technology has been marketed to consumers globally, the industry has sought a performance standard to quantify the scale-reduction ability of these water treatment devices. 

The International Association of Plumbing and Mechanical Officials’ (IAPMO) Standards department, working with industry professionals, agreed to take on the challenge of creating an American National Standard Institute (ANSI) standard to fulfill this industry need. The process was initiated when IAPMO filed for the new standard’s development through ANSI’s Project Initiation Notification System (PINS) in August 2007. A working group was put together and numerous meetings were held over an 11-year period. The IAPMO/ANSI Z601 standard was published in July 2018. 

Z601 Scope 

The working group determined the scope of the Z601 standard to include testing of devices that have the potential to reduce encrusted scale in residential water heaters, both tank and tankless type heaters, and associated plumbing downstream of the water heater. To encourage competition among manufacturers and for the benefit of consumers, the definition of a “device” has intentionally been left open so that any appropriate mean and method with the effect of reducing scale can be tested for its effectiveness. This scope allows all scale-reducing devices—physical, electronic, magnetic and more—including cation exchange water softeners, the opportunity to be evaluated to the test protocols to quantify their scale-reduction capabilities. 

Scale-Reduction Test Protocol 

Four test stations are required to conduct the test protocol. Prior to using the stations, they are tested to establish the similarity of scale production in each station (i.e., the calibration test). After the test stations have been calibrated, the devices are conditioned and installed on two of the four stations. The devices are tested for a minimum of 10 days, simulating flow patterns in a typical household. The challenge water hardness level is 26 grains per gal and includes natural elements that would be present in most tap water. The scale produced in the two test stations—including water treatment devices—is compared to the scale produced in the two control, or untreated, stations. The devices are required to reduce the scale by at least 70% to pass the protocol. In addition, to validate the test each time it is run, the scale produced in the control stations is compared to the scale produced in the original four-station calibration test conducted to validate the similarity of the scale production at the beginning. 

In addition to the scale-reduction performance test, this standard also requires that the scale reduction device be tested for structural integrity (NSF/ANSI Standard 42) and material safety (NSF/ANSI 42 or 61) in accordance with NSF/ANSI 42 or NSF/ANSI 61.

Test Protocol Brief

Section 4 of the standard covers toxicity, electrical and structural integrity requirements. Materials and components of the scale-reduction device(s) that contact drinking water shall comply with NSF/ANSI 61 or NSF/ANSI 42. These standards include a toxicological assessment of the materials that make up the product in contact with water in order to determine the appropriate list of chemicals that may extract into the drinking water. 

The allowable levels for contaminants that extract from the device are published in the applicable NSF/ANSI standards. If a chemical exists and there is not a published safe (allowable) level, a risk assessment shall be conducted in accordance with NSF/ANSI 61 Annex A to establish the allowable level for the contaminant. 

Structural integrity testing is required on products that include pressure-bearing components. This test has been designed to ensure the product can hold up to normal water pressure and typical water hammer experienced in U.S. households. Product(s) that include electrical components also need to comply with the applicable electrical safety standard(s) e.g., UL 73, 508, 979 1951 or 60335-1 specified in the electrical codes. 

Section 5 covers the general testing conditions and test specimens. The standard requires testing to be conducted on a scale reduction device that represents the product sold in the market. Manufacturers also must disclose if a change is expected in the following paraments: alkalinity, conductivity, hardness, Langelier Saturation Index, pH , zinc or any other characteristic of the water treated by the scale-reduction device and whether this change is only during the initial use of the device, has a limited capacity, or is a permanent characteristic of the device. The water used for conducting the tests is prepared from deionized, reverse osmosis-treated water to which chemical reagents shall be added as necessary.

Test procedures have been established for the following device types:

  • Scale-reduction devices without significant water characteristic changes;
  • Scale-reduction devices with significant water characteristic changes;
  • Scale-reduction devices with in-place regeneration;
  • Scale-reduction devices with sacrificial media or media with a volumetric capacity; and
  • Scale-reduction devices with direct injection of an active agent. 

Section 6 describes the scale-reduction test protocols for evaluating devices intended to reduce scale in tank-type water heaters. One of the key differences between the Z601 test protocol and the German DVGW standard is the required power density used for the heating element. Traditional residential water heaters include gas-fired and electric tank-type water heaters, which use heating elements definable power density. Electric water heaters in the U.S. have heating elements with power densities that typically range between 23 and 36 W/cm². Gas-fired tank-type water heaters have power densities that typically range between 2 and 8 W/cm². The standard allows companies to define their intended application. Devices tested at 8 W/cm² shall be deemed adequate for gas-fired tank-type water heaters, devices tested at 30 W/cm² are deemed adequate for all tank-type water heaters. Also, products tested at power density between 8 and 30 W/cm² shall be deemed adequate for use in electric tank-type water heaters when information on appropriately rated electric heating elements that operate at the tested power density or less is included.

Section 7 describes the scale-reduction test protocol for evaluating devices intended for tank-less water heaters. Residential gas-fired or electric tank-less water heaters have power densities that typically range between 23 and 45 W/cm²; the power use of such a water heater is more commonly expressed in kW (BTU/h). These devices have a power input of typically 58.6 kW. 

Section 8 describes the procedures for the calibration process, the acid washing procedure used to determine the amount of scale in each station, the calculation used to determine the percent reduction of scale in the test stations, and the required contents of the test report. 

Section 9 outlines the required product marking and the data required to be in the product literature. Installation and maintenance instructions are required to include: 

  • Scale reduction performance claim;
  • Power density; 
  • Recommended application(s);
  • Warnings on human health;
  • Volumetric capacity (if applicable);
  • Active agent usage rates (if applicable);
  • A statement that synthetic water was used for testing; and
  • If applicable, scale reduction devices intended for electric tank-type heaters tested at a power density less than 30 W/cm2 shall include a statement indicating that the appropriately rated electric heating elements that operate at the tested power density or less are necessary to achieve the claimed performance.

For decades consumers, regulators, engineers and plumbing inspectors have requested a performance standard for water treatment devices that make a scale reduction claim. Because some areas of the U.S. recently have banned the use of cation exchange water softeners, the need for this standard is even higher. IAPMO’s standards staff, Plumbing Standard Committee and the Z601 Working Group have worked diligently for the past 11 years to make this standard a reality. We encourage companies to evaluate their products in accordance with the newly published standard to substantiate their scale reduction performance claims. 

About the Author

Tom Palkon

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