What is Hard Water?
A discussion to answer this question can not be had without reference to the WQA (Water Quality Association) as the WQA is the defacto water treatment industry association and education leader. We will look at how the WQA defines hard water on it's web site. We will also look at the AWWA (American Water Works Association) definition of a softener.
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."
The part of the definition to focus on and keep in mind is how the term hardness was originally applied. This is what maters to consumers of water and it describes how the water 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:
This degree of hardness standard is often misinterpreted and arguably misleading in that it does not account for how the water behaves. It does serve to indicate how hard water will behave with different amounts or concentrations of untreated hardness minerals. For instance, less than 1 grain untreated mineral concentration will not have too much effect on how the water behaves. And 1 to 3.5 grain will have more effect on how the water behaves, it will behave even harder. If the water contains more than 10.5 grain untreated mineral concentration will display the most evident hard water behavior. All that is needed to improve the meaning of this standard is to add a simple statement to clarify this standard refers to untreated concentrations of minerals.
This degree of hardness standard often leads to confusion. Here is why, it is common practice in the water treatment industry to perform a "hardness test" to determine mineral concentration. Nothing wrong with knowing the mineral concentration. The confusion comes in when the mineral concentration measured by the hardness test is equated to the above degree of hardness standard, again this standard does not consider how the water behaves.
On another note: Standard S-339 was withdrawn from publication in 2000. The American Society of Agricultural and Biological Engineers does not support the information within the standard as being current or relevant
More from the WQA website:
What causes hard water?
Hardness minerals – calcium and magnesium – are in plentiful supply. While they are not found in their elemental form in the earth, they occur in combination with other elements in an abundance of forms. Common calcium minerals include chalk, limestone, and marble. These substances are chiefly calcium carbonate (CaCO3) or mixtures of calcium and magnesium carbonates and other impurities. The hardness in water that is caused by calcium, magnesium, and other cations is usually described in terms of the calcium carbonate equivalent.
How is hard water treated?
Softening hard water can mitigate many of its objectionable effects. Water softening can be done either at point of entry or point of use. One of the unique advantages offered by point-of-use water softening is the opportunity for homemakers to have either hard or soft water for drinking. This choice is not available if the water supply is softened municipally. Hardness minerals can be reduced in water to make it “softer” by using one of three basic means:
- Chemical softening—lime softening, hot and cold; lime-soda softening
- Membrane separation softening—Nano filtration
- Cation exchange softening—inorganic, carbonaceous, or organic base exchangers
Softening water for home needs is done almost exclusively through the use of cation exchange.
All considered this is good information but in dire need of updating. It simply does not reflect advancements to treatment processes and material improvements or current practice of water treatment. Chemical softening needs to be expanded to include polyphosphates. According to the AWWA (American Water Works Association) "polyphosphates are water softeners" (James M. Symons et al. 2000. The Drinking Water dictionary. Denver CO. American Water Works Association. Page 472).
As of 2019 it is agreed that softening water for home needs is done almost exclusively through the use of cation exchange (salt-based softener). This is changing with advances in polyphosphate softening but the water quality industry, mostly the WQA and it's affiliates, have not kept up with the pace of industry change, they do not currently recognize the difference between the concentration of minerals and the way water behaves.
What is Hard Water Summary
- When asking "what is hard water" the answer is not as simple as a measurement of the concentration of minerals.
- Hard water or hardness describes a behavior of water.
- Mineral concentration does equate to whether water displays the common qualities of hard water.
- The WQA has not kept up with changes in water treatment methods that do not require removal of hardness minerals to soften water.
- An industry standard hardness test describes the concentration of minerals in water not how the water behaves.
- A standard hardness is still a valuable way to determine whether a salt-based softener is functioning or performing to expectations.
- Water can be softened by chemical, membrane and cation exchange.
- There are treatments for hard water problems beyond salt-based softeners. Chemicals used for softening include lime and polyphosphates.