What Does a Hardness Test Really Tell Us?

What Does a Hardness Test Really Tell Us?

The answer to this question is simple but can not be fully understood or appreciated without a discussion involving the following organizations and how they are related to the interpretation of test results:

  1. The WQA (Water Quality Association). The WQA is the defacto water treatment industry association and education leader in the United States.
  2. The ASAE (American Society of Agricultural Engineers). The ASAE wrote the Uniform Classification for Water Hardness standard S-339. The standard is not currently valid since it has not been maintained since 1999 but it is still used by the WQA.

Definition of hard water:

To begin learning exactly what a hardness test tells we will examine how the WQA defines hard water on it's web site. Please note: for the remainder of this article everything in blue italic text below comes directly from the WQA web site.

"Hard water is a common quality of water which contains dissolved compounds of calcium and magnesium and, sometimes, other divalent and trivalent metallic elements. The term hardness was originally applied to waters that were hard to wash in, referring to the soap wasting properties of hard water. Hardness prevents soap from lathering by causing the development of an insoluble curdy precipitate in the water; hardness typically causes the buildup of hardness scale (such as seen in cooking pans). Dissolved calcium and magnesium salts are primarily responsible for most scaling in pipes and water heaters and cause numerous problems in laundry, kitchen, and bath. Hardness is usually expressed in grains per gallon (or ppm) as calcium carbonate equivalent." 1

Note how the term was originally applied, it describes how water containing untreated hardness minerals behaves.

The WQA definition of hard water goes on as follows:

The degree of hardness standard as established by the American Society of Agricultural Engineers (S-339) and the Water Quality Association (WQA) is as follows:

The table above is found within S-339. What does the table tell us? It tells us how we can expect water with different concentrations of untreated hardness minerals to behave. For instance, less than 1 grain hardness is considered "Soft" and will not have too much effect on how the water behaves. If the water contains more than 10.5 grain untreated mineral concentration it will behave "very Hard".

Full disclosure, I have purchased a copy of S-339 and have discovered the WQA does not share the full purpose and scope of S-339 in it's definition of hard water. The purpose and scope stated in section 1.2 of S-339 states the Uniform Classification for Water Hardness "is appropriate for classifying the overall hardness of all potable water supplies and other supplies which are to be softened by the ion exchange process". This means application of the standard is limited, it is not applicable to water to be softened by methods other than ion exchange.

So, what does a hardness test really tell us?

A hardness test simply measures the concentration of hardness minerals in the water. That's it, that's all it tells us, it does not tell us anything about how the water behaves - how soft or hard. In 2015 I set out to discover why the WQA does not recognize any treatment for hardness other than removal.

Why the WQA's definition shift from behavior characteristics to mineral concentration characteristics? It may be to move from a subjective to objective measurement. It's easy to understand water with little to no hardness minerals will behave soft. A hardness test determines the concentration of hardness minerals and is helpful in creating an understanding of the water. Measuring hardness pre and post ion exchange softening would also indicate whether or not treatment is effectively removing hardness. Unfortunately the WQA ignores, and has done nothing to clarify, the scope, of S-339 limiting application to the ion exchange softening process.

To much surprise, during my research, I discovered the WQA knows it has a problem. I found they has grappled with alternative hardness treatments and definitions for decades.2 The WQA has even had several committees over the years tasked to solve this problem, all have failed.3

Why, after decades of committees, hasn't the WQA clarified it's definition of the Uniform Classification for Water Hardness for it's membership and public consumers of water treatment. Asking this very good question ruffles more than a few feathers in industry. I have found the whole topic very polarizing with some thinking I'm threatening them and others getting very angry when their understanding is questioned. I also find very few actually know S-339 exists and even fewer know the limits of it's purpose and scope.

The ion exchange sector of the water treatment industry is happy with current definitions and standards which neatly protect established ion exchange softening business while creating a barrier to market entry by advanced treatments that alter mineral behavior. This has consequences that are not so good for consumers, the industry as a whole or our environment.  By not adapting to advances in treatment the WQA is limiting consumer choices, choices that may be better for the consumer and our environment.

One might ask this valid question; What's the real reason the WQA hasn't been able to adapt? Are advanced hardness treatment options threatening the industry status quo? Perhaps the answer can be found in where funding comes from or what industries are represented by the WQA board of directors over the years?


No convenient test currently exists for treatments that alter the behavior of the minerals without removal of the minerals. We can't currently objectively measure and prove successful treatment. Why not let the marketplace, the consumers who buy water treatment, speak for itself? A treatment that doesn't work won't last long. The WQA uses this lack of a test as a big stick to keep alternatives away from the market.

The original definition of hard water is now largely ignored in favor of the WQA's representation of the S-339 standard and is, at the very least, a disservice to members of the WQA and the public it serves. The uneducated consumer's choice of treatments is substantially limited by outdated, inaccurate and poorly maintained definitions and standards.

To this I say only two things need to happen:

  1. Modify and improve the definition of the Uniform Classification for Water Hardness to show it refers to untreated hardness minerals. And, it does not apply to softening technologies that alter mineral behavior.
  2. Focus on the original definition of hard water, the way it behaves. If the water acts hard it is hard, if it acts soft it is soft - pretty simple.


In regards to the Full S-339 Uniform Classification for Water Hardness; The standard applies to ion exchange softened water only.4

A hardness test and S-339 are excellent measures the effectiveness of an ion exchange softener.

The WQA has changed the title of S-339 from "Uniform Classification for Water Hardness" to "Degree of hardness standard" in it's literature.

S-339 has not been maintained since 1999. This means the standard is not valid.

Much of the content of this blog was learned during and subsequent to a meeting with Pauli Undesser, WQA Executive Director and many other industry leaders during the annual WQA conference and trade show being held in Nashville, TN. in March 2016.


  1. WQA website link "What is Hard Water?".
  2. Pauli Undesser, Water Quality Association Executive Director: 3/15/16 Nashville TN
  3. Pauli Undesser, Water Quality Association Executive Director: 3/15/16 Nashville TN
  4. American Society of Agricultural Engineers; Standard S339, Uniform Classification for Water Hardness, April 1977

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