Boiling aluminum in high-alkalinity water

This question ultimately relates to brewing beer, but more specifically to water treatment before brewing.


Though I can't get a water quality report, I suspect I have high levels of bicarbonate alkalinity in my tap water because boiling it causes a white precipitate (which I think is calcium carbonate) to form. I base this assumption on this formula, in the book [Brewing](https://books.google.com/books?id=cr9Pv0gefCQC&printsec=frontcover&dq=brewing&hl=en&sa=X&ei=KKbsVKr_FqzgsATMhIGQCw&ved=0CBQQ6AEwAA#v=onepage&q=brewing&f=false): 


$$\ce{Ca(HCO3)2 ->[heat] CaCO3 + CO2 + H2O}$$


I wanted to sanitize some aluminum foil so I boiled it in fresh tap water for about 15 minutes. I noticed a few things:


* The precipitate formed much faster than it normally would without foil in it.
* The foil began to blacken in certain parts.
* I'm not positive, but the precipitate seems a bit finer in texture than it normally is.


I thought at first maybe the foil was just providing nucleation points for the carbonate to form around. But then I thought I remembered reading somewhere that aluminum competes with calcium in certain situations (I think it was regarding osteoporosis, maybe). The question I have, then, is whether or not it's feasible that aluminum could be affecting a different reaction than what I'm assuming normally occurs in this situation?




It appears your creating [calcium aluminate](http://en.wikipedia.org/wiki/Calcium_aluminates) by reacting aluminum with alkaline water. Since that is probably *not* wanted in the brew, you might use glass or *anodized* aluminum, which is more resistant to chemical attack, and a water softener, if the calcium carbonate isn't wanted, either.


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