By Rick Andrew
Almost everyone who reads this column will know what a water softener is, and many of you are well versed in their installation and operation. Further, many of you know that residential softeners may be certified to Standard 44. But most of you are probably unfamiliar with the details regarding Standard 44 scope and requirements. Is there a size cutoff on what’s considered to be a residential softener? What testing is involved? Is there a way to address families of softeners that use the same control valve, but vary in resin tank size and amount of resin used?
The purpose of this column will be to answer these questions and others; to help explain the conservative testing requirements and other nuances of a standard that addresses the products we are all so familiar with. All of these requirements add up to a ‘hard’ standard for softeners, indeed.
Residential vs. commercial softeners—where is the distinction?
NSF/ANSI 44 defines a residential softener as one with conventional plumbing fittings not exceeding 1.25” NPS (nominal pipe size). So, any softener with an inlet exceeding 1.25” is not considered residential and falls outside the scope of the standard. Notice that the definition is not related to resin tank size or amount of cation exchange resin: it is based solely on the inlet size.
I’m sure there are some softeners with larger control valves serving large residences out there and I’m also sure there are some softeners with 1.25” inlet valves serving some commercial or institutional operations. Separating residential from non-residential applications will always result in some exceptions, especially in this day and age of very large homes. But the approach of basing the distinction on control valve inlet size is one that is very simple, clear and reasonable in terms of how it correlates with usage in the field.
Other scope issues
The definition of a residential water softener in Standard 44 also specifies that it must be a cation exchange system and it must be regenerable with salt brine. The regeneration may be manual or automatic (although I don’t believe too many manual regeneration cation exchange softeners are being sold these days!).
I sometimes get questions about magnetic anti-scale devices or scale-inhibiting physical water conditioners. These devices fall outside the scope of Standard 44, because they do not use a cation exchange technology. So they cannot be certified to Standard 44.
I have also received inquiries about whether disposable cartridge filters containing cation exchange resin could be certified as softeners under Standard 44. These devices also fall outside the scope of the standard, because although some do use cation exchange technology, they are not regenerable.
Testing requirements
There are actually several different tests required under Standard 44, each designed to evaluate a different aspect of the softener. A summary of these testing requirements is included in Figure 1. 
A formulation review and material extraction test is required to establish that no contaminants leach from the softener at concentrations of toxicological concern. Fifteen minute hydrostatic and 100,000 cyclic tests are required to establish the long-term durability of the system, as well as its resistance to pressure spikes. A pressure drop test confirms that the softener will not cause a drop of more than 15 psi in line pressure when operated at the manufacturer’s rated service flow.
The capacity of the softener is established by testing it at one-half of the manufacturer’s rated service flow, using water that has a hardness of 20 ± 2 grains per gallon. Capacity testing is required at the lowest and highest salt settings and the setting closest to the midpoint of the range. Capacity for other salt settings is interpolated from the three measured capacities. Each test of capacity is conducted by regenerating with an exactly measured amount of saturated brine, bypassing the softener’s brine delivery system. This makes the capacity determination as accurate as possible because the regeneration is as exact as possible. The endpoint of the test is defined as one grain per gallon breakthrough. The leakage throughout the run is subtracted off when the capacity is determined. Three successive runs within 10 percent of the average of the three runs are required, with the average value being considered the official capacity at that salt setting. See 
Figure 2 for a graph of an example capacity run.
During capacity testing, the amount of residual chloride in the product water is measured after regeneration. The net chloride contribution from the softener may not exceed 100 mg/L, indicating that the rinse is sufficient. Also, a separate test known as ‘softening performance’ is required, involving regeneration of the softener at the lowest salt setting and operating it 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 one grain per gallon for any of these samples.
Because the brine system is not used when conducting capacity testing, accuracy of the brine system must be determined through a separate test. This testing is conducted at the lowest and highest salt settings, and the setting closest to the midpoint of the range, similar to capacity. It involves weighing the brine tank before and after regenerations and three successive runs within 15 percent of the nominal salt setting must be achieved. There is an alternate procedure that may be used for time-controlled brine systems, involving calculations based on saturated brine.
Efficiency
Most wise readers are aware that softener efficiency is very important, at least in some key markets. Although efficiency is not required for certification to Standard 44, it may be required by state or local regulations. Efficiency is related to the amount of hardness capacity per amount of regenerant salt and per volume of regenerant water. Inefficient softeners require more salt and/or regenerant water to achieve the same amount of softening capacity as more efficient softeners.
Also, the efficiency of a softener varies with the amount of salt used for regeneration. The more salt that is used to regenerate the softener, the less hardness capacity per amount of salt. There are diminishing returns for using more and more salt. In fact, after a point, additional salt used in regeneration will not achieve any more softening capacity and will simply be rinsed out of the system.
Efficiency is based on calculations of data measured and recorded during capacity testing. The requirements for efficiency are included in Figure 3. 
Note that only demand initiated regeneration (DIR) softeners may claim efficiency. A softener must achieve both salt efficiency and water efficiency in order to be ‘efficiency rated.’ Also, the salt setting must be included in any efficiency specifications or statements by the manufacturer. The State of California has a more stringent requirement for efficiency ratings, requiring at least 4,000 grains of capacity per pound of regenerant salt.
An approach to families of softeners—conformance by calculation
Standard 44 includes procedures to calculate pressure drop, capacity and efficiency for softeners that are similar to the test unit. The requirements for softeners to be considered ‘similar’ include usage of the same control valve and distributor (although length of distributor tube can vary with size of resin tank), as well as limitations on variation in cation exchange resin and amounts of resin, resin tank size, regeneration volumes and flow rates, rated service flows and salt dosages.
The concept is that a line of softeners built with the same control valve can be certified based on testing one or a few of them and then using calculations included in the standard to calculate pressure drop, capacity and efficiency for the non-tested models. The equations used for calculations have proven accurate in practice. Conformance by calculation allows manufacturers to certify broad lines without having to test each unit separately.
A ‘hard’ standard for softeners
As you can see from this brief overview, Standard 44 requires testing all relevant aspects of water softeners, from material safety to accuracy of the brine system. Given the numerous tests and conservative criteria required to establish conformance of a softener to the standard, it is certainly not an ‘easy’ standard. And for manufacturers seeking efficiency ratings on top of all of the requirements, it can become downright ‘hard’.
About the author
Rick Andrew has been with NSF International for over six years, working with certification of residential drinking water products. He has been the Technical Manager of the Drinking Water Treatment Units Program for over three years. His previous experience was in the area of analytical and environmental chemistry consulting. Andrew has a bachelor’s degree in chemistry and an MBA from the University of Michigan. He can be reached at 1-800-NSF-MARK or email: [email protected]