Why does water need to be softened? Water needs to be softened to remove minerals, such as calcium and magnesium, which build up and clog taps and water supply systems. Depending on where you live, you may or may not need a water softener. This is because of the geology and the rocks that the water flows through.
Water is obviously made up of hydrogen and oxygen, and it is a liquid, so describing it as hard might be a bit confusing. Even hard water is still a liquid and conforms to all the rules that govern liquids. However, hard water carries far more minerals than soft water, and this is where the hard and soft definitions come from. Water picks up minerals because it is known as a universal solvent. It is called this because more substances will dissolve in water than in any other liquid. There are two reasons for this. Firstly, the hydrogen side of any water molecule carries a slight positive charge, and the oxygen side carries a slight negative charge. That means a water molecule can attract almost any other molecule, no matter whether it is positive or negative. Secondly, the hydrogen and the oxygen in water molecules are held together by covalent bonds. That means they share their electrons, and it is a strong bond. Many other substances are connected by an iconic bond, which is where the atoms are just attracted to each other. When a substance is mixed with water, the negative side sticks to the hydrogen, the positive side sticks to the oxygen, and the covalent bond is stronger than the ionic bond, and it pulls the other molecule apart.
When water flows through rocks, before it is treated and gets into our water systems, it picks up lots of minerals on its way. These minerals are dissolved in the water and carried along with it. Some areas have harder water, and some areas have softer water because of the makeup of the geology of the groundwater. Some rocks are much higher in soluble minerals. The water goes through our plumbing and out of our taps, where we use it. Water with all of these minerals in it is perfectly safe because the minerals it picks up are minerals our bodies need. The problem comes when the minerals come into contact with the metal pipes the water flows through.
One of the main minerals that is dissolved in water is calcium, and this is the main culprit. It builds up on the inside of pipes, where it is known as limescale. It is more likely to build up on pipes that carry hot water, but it builds up in cold water pipes as well, it just takes longer. You may see it in your kettle as well. It is most common in hot water because when you heat the water, the molecules gain more energy, and it becomes harder for the water to hold onto the minerals. They drop out and stick to the nearest surface, which is the metal of the pipe or the bottom of the kettle. The minerals can fall out of cold water as well, but it takes a lot longer.
When the limescale sticks to the surface of a pipe, it starts to build up and becomes thicker. As the buildup increases, the pipe becomes narrower and which reduces the water pressure. It can eventually block pipes. If it builds up in a kettle, it can cover the heating element and reduce the efficiency of the kettle. The limescale can also increase the rate at which metal pipes corrode. Interestingly, hard water also doesn’t stick to soap as easily, so you need more soap when you want to wash or shower.
To soften water, you need to remove the minerals that are dissolved in it. The easiest and most common way of doing this is by ion-exchange. This process passes the water through a resin filter that contains sodium ions. The resin molecules are covered in sodium ions. However, the resin prefers calcium and magnesium molecules far more than sodium ions, so they are more strongly attracted to the resin. When water flows through the filter, the molecules basically swap, and the water loses its calcium and magnesium and picks up sodium. The water has been softened. The filter lasts until all of the sodium ions have gone, and then it has to be replaced. And this is what I learned today.
Sources
https://extension.psu.edu/water-softening
https://www.calgon.co.uk/am-i-affected-by-hard-water/hard-water-vs-soft-water
https://www.thoughtco.com/why-is-water-the-universal-solvent-609417
https://www.thoughtco.com/definition-of-covalent-bond-604414
https://www.thoughtco.com/definition-of-ionic-bond-604536
https://en.wikipedia.org/wiki/Limescale
https://en.wikipedia.org/wiki/Water_softening
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