Hardness and Softening – Cliffs Notes

Resin Lesson 1

Most folks know that water softening is used to fix hard water. But what exactly is hard water, and what is softening, and how does it fix hardness. First off let’s address hardness.

  • Hardness is made up of Calcium and Magnesium. Hard water causes scale build up and spots after rinsing
  • Iron often accompanies hardness and allows bacteria to grow and rust issues to occur
  • Water Softening is the most popular way to remove hardness.

The functional unit of a water softener is called cat-ion resin. This appears as a gel-like, plastic bead. Similar to sand but always moist and softer to the touch than sand. Each individual resin bead is a 3-dimensional sphere with countless nooks and cranny’s inside the bead. The bead is made of styrene and divinyl benzene.

In the manufacturing Process something called a functional group (R) is attached to the resin. In the case of water softening this functional group has a negative charge. It is designed to attract and hold elements (ions) with a positive charge. (Figure 1).


When the resin is soaked in a heavy salt stream, also called regeneration, the functional group holds on to the sodium ion, represented as Na+. Then, once the softener is placed into service, the hardness ions in the tap water (Ca++ and Mg++), because of what is called stronger electronegativity, replace, or “knock off” the sodium ions and let them pass into the softened water. This is why some medical conditions warrant caution with soft water. Remember, the harder the tap water, the more sodium in the softened water. (Figure 2)

Finally, once the resin beads are exhausted, that is to say, unable to exchange any more hardness for sodium, a high concentration of salt water flushing, regenerates the resin and the cycle can start anew.


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