domestic water filters

[Coldicote]

I used a soil testing kit in the garden to check for acidity. It had dip tabs and a colour chart for reading results. It could also be used for testing water, so I experimented.

Ordinary tap water showed neutral as one might expect; rain water showed very slightly towards acid; my cup of tea (not surprisingly) showed acid. Water from a domestic jug filter, using a well known filter cartridge, indicated most acid of all - a strong red colour that went off the end of the scale. Probably OK, but why? Are there any science wizards out there who can explain please?

[Law Student]

Your filter probably contains an ion exchange resin; it works by replacing metal ions with hydrogen ions and making the water acidic.

e.g. CaCl2 is replaced by 2xHCl.

[Coldicote]

Thank you for this knowledgeable answer. I'm wondering if years of using 'acidic' water might have any long term health effects - maybe good, maybe not. I'm not a science minded person but this is interesting and I'll explore further.