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this post was submitted on 15 Feb 2024
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Chemistry
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Ah, I wondered if I needed to explain that, since dishwashers in N.America do not take salt. European dishwashers tend to have built-in water softeners (because it’s somewhat uncommon to have whole house water softeners). So we periodically have to fill a salt reservoir in the dishwasher to feed the water softener.
Ah, ok. I was familiar with water softeners needed for homes with well water, but it didn't occur to me that soft water would be a problem for dishwashers. Thanks!
Well it’s not actually clear to me whether the soft water is to protect the dishwasher, or to make cleaning more effective. Soft water dissolves soap better which makes it more effective in cleaning. It also means I can use powdered detergent (which is cheaper than liquid detergent, but in hard water powder doesn’t perform as well). Soft water has the down side that it’s actually /more prone/ to corrosion than hard water (at least according to youtube plumbers). So I’m tempted to conclude the built-in water softener is just for cleaning effectiveness.
My understanding is that every mole of water hardness (mostly Ca^2+) reacts with two moles of soap to produce soap scum. So using softened water (replacing Ca^2+ with 2Na^+) allows you to use less soap and reduces soap scum buildup.