Water Filters Effect on Brewing Water (by Jon Stika)
Activated charcoal (carbon) should reduce Cl significantly and may affect SO4 (as it also has a negative charge and high molecular weight) but I don’t believe it will affect Ca, Mg, Na, and HCO3 significantly even though HCO3 does carry a negative charge. HCO3 and Ca typically will buffer each other, so if a little HCO3 is removed by the activated carbon filter, it will “bounce back” after the filter if the water is the same pH.
The positively charged Ca, Mg, and Na ions should go right through the filter and activated carbon. Ca is a good thing for brewing (yeast nutrition), Mg really doesn’t make much difference unless it’s really high and then will have a laxative effect (oh no), Na isn’t a hugh issue unless it is high and in combination with a high SO4 concentration then it will make give beer a nasty harshness (this is the problem I had with Patterson Lake water and to a lesser degree with SW pipeline water). Cl as an ion lends some sweetness to beer, but as a gas (Cl2) or trihalomethane gives a “cholrinated swimming pool” taste.
So I believe your filter will knock down the Cl taste if it has activated carbon, may reduce SO4 some, but will have little effect on the rest of the major ions.