One thing I'll point out out about not needing to boil top-off water.
The yeast we pitch is alive and therefore gives your wort an immune system; a Wyeast smack-pach has upto a 100 billion cells. So most bugs just can't compete. In comparison, nasty tap water may have a few hundred bugs in it, Yes, there are bugs that can compete with yeast, like lactobacillus, but for the most part tap-water bugs are a non-issue.
Think of the bacteria in untreated leap-water like bear. Really bad news in the unpopulated (unpitched) boonies. If you see one, you better move cautiously in the other direction; known bear habitats are not great places for pitching a tent. Once you pitch yeast in your wort though, the microscopic lasdscape is like downtown Manhattan, only more so. What chance does a bear havet there? Even a hundred bear? Snowball's chance in hell really. Sure, a bunch of people may die before the bear infestation is resolved. But I can assure you, Manhattan is not worried about bear attacks.