By Rick Andrew
The point-of-use (POU) and point-of-entry (POE) water treatment industry considers water softeners to be a key element of its overall water solutions portfolio because of the value they provide for end-users with hard water. In many areas of North America and beyond, hard water is common, especially in certain regions such as the Great Lakes region. Water softeners are also highly engineered pieces of equipment, designed and constructed to provide end-users with years of reliable and efficient service.
A holistic evaluation of multiple aspects of water softeners is offered under NSF/ANSI 44 Residential Cation Exchange Water Softeners, allowing manufacturers, distributors, end-users, and regulators to be confident the equipment they’re using conforms to the standard.
A Standard for Residential Softeners
There are applications for water softeners in residential, commercial, and industrial settings. The scope of NSF/ANSI 44 specifically covers residential applications, so it is important to clearly define “residential.” NSF/ANSI 44 defines a residential softener as a regenerable cation exchange system intended for residential use with conventional plumbing fittings not exceeding nominal pipe size of 1.25 inches. Under this definition, any softener with an inlet exceeding 1.25 inches is not considered residential and falls outside the scope of the standard. Note that the definition is not related to resin tank size, amount of cation exchange resin, or system salt settings. It is based solely on the inlet size.
Testing Under the Standard
Figure 1 summarizes the testing requirements of NSF/ANSI 44. Material extraction testing is required to establish that contaminants do not leach from the softener at concentrations of toxicological concern. Structural integrity tests include 100,000 cyclic and 15-minute hydrostatic evaluations to establish the long-term durability of the system, as well as its resistance to pressure spikes. Pressure-drop testing confirms that the softener will not cause a drop of more than 15 pounds per square inch (psi) in line pressure when operated at the manufacturer’s rated service flow.
Capacity of the softener is based on specific salt settings and determined by testing at half of the manufacturer’s rated service flow. The feed water for this testing has a hardness of 20 ± 2 grains per gallon. The standard requires capacity testing at the lowest and highest salt settings, and the setting closest to the midpoint of the range of salt settings. Interpolation can be used to determine capacity for other non-tested salt settings. Extrapolation beyond the tested range is not permitted by the standard, so testing at the low and high salt settings is critical.
Capacity tests start by first regenerating with a precisely measured amount of saturated brine. Measured saturated brine is used instead of the softener’s actual brine system to reduce variation in the amount of regenerant salt from the intended salt setting, which can cause variation in the tested capacity. Breakthrough of 1 grain per gallon in the softened water defines the endpoint of the test.
The standard also accounts for hardness leakage by requiring measurement of the hardness in the softened water throughout the test. The test is run multiple times; three successive runs within 10 percent of the average of the three runs is required.
The average capacity value from these three runs is considered the official capacity at that salt setting.
The amount of residual chloride in the softened water is measured after regeneration. The net increase in chloride concentration from the softener may not exceed 100 milligrams per liter (mg/L). This confirms that the rinse is sufficient to rid the softened water of excess salt.
A softening performance test is also required. For this test, the softener is regenerated at the lowest salt setting and operated at the manufacturer’s rated service flow. Samples of product water are taken each minute for 10 minutes, and the hardness of the water may not exceed 1 grain per gallon for any of these samples. This requirement ensures that the softener is being regenerated to effectively treat a minimum amount of water without excessive leakage at the rated service flow.
The accuracy of the brine system must also be tested. This testing is conducted at the lowest and highest salt settings, and the setting closest to the midpoint of the range. It requires placing the brine tank on a scale and weighing it before and after regenerations to determine the amount of salt used. The test must be run multiple times, and three successive runs within 15 percent of the nominal salt setting must be achieved.
For example, a successful test of a 10-pound salt setting would require the weight of the brine tank to decrease by 8.5 pounds to 11.5 pounds after each regeneration for a series of three regenerations. There is an alternate procedure involving calculations based on saturated brine that may be used for time-controlled brine systems.
Softener Efficiency
Water softener efficiency can be established for demand-initiated regeneration (DIR) water softeners, but not for other softeners. Efficiency is based on two factors:
- The hardness capacity per amount of regenerant salt.
- The capacity per volume of regenerant water.
More-efficient softeners require less salt and regenerant water to achieve the same amount of softening capacity compared to less-efficient softeners. Although efficiency is optional according to the standard, it may be required by state or local regulations.
Efficiency varies with the amount of salt used for regeneration. The higher the salt dosage, the lower the salt efficiency. There are diminishing returns in terms of softening capacity for regenerating with more and more salt. Ultimately, there is a saturation point at which additional salt used in regeneration will not achieve any more softening capacity and will simply be rinsed out of the system during regeneration. For this reason, efficiency ratings are always associated with specific salt settings.
Efficiency is calculated from data measured and recorded during capacity testing. The minimum requirements for softeners to be considered efficient are included in Figure 2. A softener must achieve the criteria related to both salt and water at a given salt setting to be efficiency rated. Also, any efficiency specifications or statements in the product literature or advertising must refer to the salt setting at which the efficiency was achieved. It is possible—and actually likely—that a softener can be efficiency rated at certain salt settings but not at others. Of note: California has a more stringent requirement for salt efficiency ratings than does Standard 44, requiring at least 4,000 grains of capacity per pound of regenerant salt.
NSF/ANSI 44 Includes Conformance by Calculation
The standard includes procedures to calculate pressure drop, capacity, and efficiency for softeners that are similar to the tested model but not actually tested themselves. There are specific requirements for softeners to be considered similar, including:
- Identical control valve.
- Identical distributor (length of distributor tube can vary with size of resin tank).
- Limitations regarding:
» Variation in cation exchange resin specifications.
» Amount of resin.
» Size of resin tank.
» Regeneration volumes.
» Flow rates.
» Salt dosages.
Using this approach, a family of softeners built with the same control valve but varying in tank size and media volume can be evaluated to the standard based on testing one or a few of them. Formulas included in the standard are used to calculate pressure drop, capacity, and efficiency for the non-tested models.
All Stakeholders Benefit from Thorough Evaluation
Testing all relevant aspects of water softeners is required by NSF/ANSI 44, including material safety, structural integrity, softening capacity, and accuracy of the brine system. The result is that a variety of tests is required, each one designed to evaluate different aspects of the softener. Evaluation of these aspects provides confidence in the functionality of the equipment for end-users, manufacturers, distributors, and regulators.
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]