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I am looking for ways of removing water hardness from tap water, specifically permanent hardness.

I have tried working on some methods, e.g., to perform precipitates using sodium hydroxide and calculated calcium hydroxide, but it seems that either my methods or something else is wrong.

Please recommend me some methods (or resources) on how to remove the hardness from tap water.

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  • $\begingroup$ What are the methods that you've been working on? $\endgroup$ – pH13 - Yet another Philipp Aug 18 '15 at 10:00
  • $\begingroup$ I tried using sodium hydroxide and calculated calcium hydroxide to form precipitates $\endgroup$ – joseph's the chemist Aug 18 '15 at 10:24
  • $\begingroup$ An ion switcher is the usual way to go. $\endgroup$ – Jori Aug 18 '15 at 13:08
  • $\begingroup$ the only sure ways are distillation and reverse osmosys (de-ionisation) . Ion-exchange resins also may be of use. $\endgroup$ – permeakra Aug 18 '15 at 16:38
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Without knowing what dissolved species are causing the hardness, it's a little difficult to know what to advise. Performing qualitative analysis would likely help you a lot.

You describe using lime softening (i.e., using hydroxides) which can help in some cases. Usually the resulting hydroxide precipitates are pretty hard to filter, requiring a membrane or a very good filtration system.

As Wikipedia notes, there are a few other reliable techniques:

  • reverse osmosis
  • distillation
  • ion exchange resins
  • chelating ligands

While the first three are definitely the best in terms of ultimate water quality, an easy thing to supplement lime softening would be to add various chelating ligands. For example, after you carefully filter the water from lime softening, maybe add citric acid?

In any case, I'd suggest you do some sort of qualitative analysis (and pH) testing as you go. This is the best way to know what steps you'll still need.

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