Any data on ppm water treatment comparing before mash and after?

[pricelessbrewing]

So I'm on biabrewer.info as well, and one of the users is passionately stating that topping off the water during the boil creates wort that tastes terrible, almost like cat pee. After a couple requests for how/why, he says it's due to the fact that mineral composition is much lower after the mash, and that boiling lowers the mineral ppm as well.

Could anyone back this up, or refute it? Preferably with something well known and recent.

 

[ajdelange]

It obviously depends on what the mash/dilution water composition is. Malt contains lots of minerals so wort is going to be much stronger in magnesium and potassium, for example, but weaker in calcium (which precipitates in the mash tun and kettle). Then there is what is ever in the dilution water. I dilute with RO water all the time. No problem. If he is diluting with swamp water what does he expect?

 

[pricelessbrewing]

That's what I was thinking exactly. As long as the water is good quality and not full of chlrone I can't think of any reason it would degrade the quality.