Myth: Descaling is the same as demineralising and alters the acidity (pH) of the water

A water softener provides limescale-free water. Limescale-free water has had only the minerals calcium and magnesium removed, whereas demineralised water has had all minerals and other solid particles removed, leaving simply H₂O, or pure water.

With softening alone, the composition of the water therefore changes only very slightly, and this prevents any change in the Total Dissolved Solids (TDS) and carbonate hardness (KH). If you were to measure both of these values, you would find that they remain the same before and after softening.

If these values are affected, the water will have a different acidity level (pH value). Acidic water is corrosive and can corrode copper pipes and other metals such as chromium. Acidic (corrosive) water must therefore never be used.

Limescale-free water is good for copper pipes

Lime-free water is actually good for copper pipes. The coarse lime in hard water actually causes the pipes to wear out more quickly than softened water, which keeps the pipes clean and smooth. This has been extensively researched and demonstrated by TNO on behalf of Aquacombi. (You can find the report by Googling ‘TNO 2012 r10424’).

So where does this myth come from?

It’s quite simple. Soft water (low in calcium) found in nature almost always has a high acidity (pH) and corrodes copper pipes and other metals (causing them to rust). Your tap water, however, is pH-neutral/non-acidic, and a water softener does not alter the pH level. So soft water produced by a water softener is neither demineralised nor acidic, and does not corrode your pipes at all.

See also: Does hard water damage copper pipes?