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:  

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

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 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.