By Tom Palkon, CWS-VI

Summary: Through a process called “conformance by calculation,” one third-party laboratory is able to incorporate a set of procedures when applying standards to water softeners. What does this mean for manufacturers? More than you think, and the industry is waiting for other standards to follow suit.

Water softeners are one of the most complicated drinking water treatment units to test and certify. Unlike most filters in which challenge water enters the unit and product water is produced for a specific amount of gallons, water softeners have the added complexity of the regeneration process. Because there are a variety of valve manufacturers, each with their own idea of the best regeneration procedure, the testing agency must have a complete understanding of the manufac-turer’s valve operations and system design before it begins testing to have any success.

Water softener standards
The Water Quality Association (WQA) and NSF International spent tremendous time and effort harmonizing NSF/ANSI Standard 44 with the WQA S-100 standard. Even though the two standards still have differences concerning the material safety criteria, all the other sections have been harmonized. A critical aspect of the harmonization process has centered on the “conformance by calculation” procedures.

About Standard 44
The water softener standard, like all the drinking water treatment unit standards, is comprised of four sections:
Materials—This section ensures the materials of a water softener in contact with the drinking water don’t extract contaminants above allowable levels when they’re exposed according to the extraction procedure.
Design and construction—This section provides several minimum design and construction requirements. Some examples of these requirements are:

  • Working pressure
  • Electrical safety
  • Waste connections
  • Performance indication devices
  • Brine tank requirements

Chemical, mechanical and structural performance—This section contains the majority of performance testing procedures and requirements. Before a water softener can be certified, it must meet a variety of performance tests. A water softener must be tested for:

  1. Capacity—Reduction of water hardness
  2. Softening performance—Deliver soft water at the maximum flow rate
  3. Rinse effectiveness—Does not add chlorides (more than 100 mg/L1) after regeneration
  4. Salt efficiency (DIR systems2)—Amount of hardness removed per pound of salt used during regeneration
  5. Water consumption during regeneration—Amount of water used during regeneration
  6. Accuracy of the brine system—Ensures that water softeners will deliver the correct volume of brine during regeneration
  7. Additional claims—Manufacturers have the option of claiming barium and radium
  8. Structural integrity—Burst tests to make sure units will handle pressure, etc., over time
  9. Pressure drop—Determines flow rate and associated pressure drop characteristics of the water softener

Instruction and information—Manufacturers must develop and provide three pieces of literature, each containing specific information that’s outlined in the standard. Installation, operation, and maintenance instructions must be made available for each system. A data plate or label shall be affixed in a conspicuous location to the system. A performance data sheet must be developed and included in pre-purchased sales literature or readily available to prospective purchasers.

Standard 44-DWTU difference
NSF/ANSI 44 is a unique drinking water treatment unit (DWTU) standard because it contains specific sections about conformance by calculation. The conformance by calculation section allows manufacturers to extend the results of a tested unit to other sizes (candidate units) of a model line. No other DWTU standard contains such procedures, although it would be ideal if they all did. Because the procedures are clearly defined in the standard, manufacturers don’t have to guess or wonder what the certification agency will require to extend test data to similar models.

Even though the water filter and reverse osmosis (RO) standards don’t contain conformance by calculation procedures, many certification agencies developed their own procedures to extend results of a tested unit to other sizes of a model line based on generally accepted scientific practices and principals. As more certification agencies enter the market, each with their own conformance by calculation procedure for filters and ROs, manufacturers have experienced different test bracketing requirements between certification agencies. Because Standard 44 spells out the specific procedure, confusion can be reduced.

The procedure
It’s important to remember that every size water softener doesn’t have to be tested for certification. If you’re thinking about certifying a line of water softeners, make sure to review the conformance by calculation procedures or at least the calculation limitations listed below. A lot of money can be saved if the manufacturer chooses the correct size water softener to test. Because some certification bodies have tremendous experience with water softener testing, they can assist manufacturer’s in determining the correct size water softener to test based on the manufacturers product line. Check with your certification agency even if you feel confident that you chose the correct water softener to test.

Calculation limitations—To extend the data of a tested water softener to a candidate water softener, each of the following criteria must be met:

  • The same type of salt is used;
  • The softener tank cross-sectional area isn’t more than 200 percent or less than 50 percent of the tested unit;
  • The cation exchange media bed depth of softeners isn’t less than 75 percent of the bed depth of the tested unit;
  • The bed depths of other adjunct media or under-bedding shall be 75 to 150 percent of that in the tested unit;
  • The maximum published flow rate of softeners per unit of cation exchange media volume isn’t more than 120 percent of that of the tested unit;
  • The slowest rinse flow rate per unit of bed cross-sectional area is 50 to 120 percent of that of the tested unit;
  • The total rinse volume of water per cubic meter (m3) or cubic foot (ft3) of cation exchange media shall be at least 2,000 liters (L)—15 gallons (gal)—or 90 percent [if less than 2,000 L/m3 (15 gal/ft3)] of the rinse volume of water per cubic meter (cubic foot) of cation exchange media in the tested unit. The total rinse volume of water per cubic meter (cubic foot) of cation exchange media also shall not exceed 200 percent of the rinse volume of water per cubic meter (cubic foot) of cation exchange media in the tested unit;
  • The salt dosage per cubic meter (cubic foot) of cation exchange media shall be within the range of tested salt dosages per cubic meter (cubic foot) of cation exchange media in the tested unit;
  • The rated capacity per unit volume of cation exchange media at the same salt dosages shall not be increased, and
  • Comparable cation exchange media in mesh size and chemical formulation shall be within ±10 percent of the particle size, crosslinking, and exchange capacity of the cation exchange media used in the tested system. This requirement shall be satisfied by providing appropriate documentation from the resin manufacturer.

If all of the above criteria of a candidate water softener have been met, then the system is eligible to use the calculation procedures outlined in Standard 44. Please note that these procedures only cover capacity and pressure drop data extensions. The procedures don’t cover material safety, brine accuracy or structural integrity. Because the procedure doesn’t cover all the required tests of the standard, some confusion still exists.

Conformance by calculation is necessary for all DWTU standards. Without these procedures, manufacturers may not be able to afford certification or they would be limited to very small product lines. The NSF/ANSI water softener standard leads all other drinking water treatment standards because it incorporates the procedures directly into the standard. This eliminates conformance by calculation differences between certification agencies. Hopefully, all DWTU standards will have conformance by calculation procedures.

NOTES: 1. milligrams per liter, 2. demand initiated regeneration

About the author
Tom Palkon is the director of product certification for the Water Quality Association’s (WQA) Gold Seal program. The WQA now certifies products to the NSF/ANSI Drinking Water Treatment Unit and Drinking Water Additives standards. Palkon has been managing the WQA’s analytical, performance laboratory, and certification program for six years. He holds the WQA’s highest Certified Water Specialist (CWS) designation, Level 6. He can be contacted at (630) 505-0160, (630) 505-9637 (fax) or email: [email protected]



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