Poison

Earlier, I was thinking about drinking water vs washing water. I'd just as soon have everything filtered, but it's not practical. When people ask me why I want my cooking water filtered too, since it's boiled, I compare it to urine. What if unfiltered water = urine. You might use it to rinse off your plates, but would you boil your food in it or use it in your soups? I think not.

(Ok, some people know that urine is actually quite sterile and that some people drink it for health benefits on purpose, but those aren't the kinds of people who ask "Why do you want filtered water for boiling?" :P )

Attempts to silence people by disgusting them aside, not all contaminants in water can be boiled away. Where I live, one of the bigger issues is rust from pipes. Do you know how much rust, lead, and other metals are removed from water when you boil it? - None. 'Nuff said.